There are quite a lot of characters in the movie, with new Autobots and Decepticons introduced, along with other characters like the Quintessons. Here's a list of them all, M.I.A Autobots are covered in the FAQ because there's way too many to list here.
As per usual, there are more Autobots featured in the movie than Decepticons, although several of them are just killed off to make way for the new guys. Although thankfully some of the new characters are good, and some of the older characters survive, and then there's Wheelie. Hmmm.
Arcee is a new character, and is one of the few female Autobots (there were some in the second season, but they only appeared in one episode). Anyway, Arcee is shown to be as strong as any of the other Autobots and can transform into a car. A toy of Arcee was planned but later scrapped, making it strange they they even bothered giving her large roles in the third season of
Transformers.
The totally rockin' Blaster is the Autobot's main man when it comes to communications, and is seen in the battle at Autobot City where he contacts Optimus Prime on Moonbase 1 in his cassette player mode. His main function in the movie however was to send out his
four new cassette robots which weren't in the second season. After the battle Blaster will later appear to receive the communication from Jazz, but he's most likely left to repair Autobot City after the two Autobot shuttles launch.
He only appears for a second or two, and his head is looking the opposite way from the camera, but Bluestreak can be seen briefly in the movie right when Kup says "What's that darn fool doing?" as Hot Rod is shooting at the shuttle. However, on closer inspection the animators have actually drawn Prowl but coloured him like Bluestreak (Bluestreak should have two shoulder cannons for a start). But lets just say he's Bluestreak for the sake of it.
Another new character introduced is Blurr, who always talks ultra fast and can move extremely quickly. It seems his vehicle mode was not upgraded to blend in with Earth, as he transforms into a futuristic hover car. He doesn't really get to do much in the movie other than follow the other new Autobots around. His voice actor, John Moschitta, once held the record for the world's fastest talker, and would also voice Blurr in both seasons 3 and 4 of
Transformers.
Brawn is suppose to be one of the toughest Autobots but this claim does not hold up in the movie, as he is hilariously defeated by one blast from Megatron's gun mode. Brawn always did suck though so I expect everyone was standing up and cheering when he got served. Twat. 
From what I can tell, Bumblebee is the only Autobot on the Autobot's second Moonbase, which he runs with Spike. Bumblebee doesn't have a major role in the movie, his only highlight being when he and Spike attempt to blow up Unicron be detonating the Moon as he eats it, but that plan fails. He is later rescued by Daniel and he along with the Autobots escape the exploding Unicron. 
Cliffjumper is a tough little Autobot but he never actually gets to do any fighting in the movie -he remains behind with Jazz on Moonbase 1 when the first shuttle blasts off, and also stays when Optimus, Sunstreaker and the Dinobots head off to Autobot City. Later on, Moonbase 1 is attacked by Unicron and destroyed and Cliffjumper is trapped inside the planet eater, but is later saved thanks to Daniel. Even though he survives the movie, this would be his last appearance in the cartoon series.
One of Blaster's new cassette robots, Eject can transform from tape to robot and makes his entrance by taking on Frenzy.
Gears does actually appear in the movie - when Ironhide spins around in his chair and runs off to head towards the shuttle, Gears is 
Grapple can only be seen in one shot during the battle at Autobot City, where he fights 
The leader of the Dinobots, Grimlock can transform into a
t-rex and enjoys getting into fights a lot. In the movie, he leads the Dinobots against various foes, such as Devastator, Sharkticons and even Unicron. Whilst he's a character introduced in the first season, he's exempt from the death list and survives the movie. 
Another new Autobot is Hot Rod, who is shown to be a bit brash and all too eager to rush into a situation without any kind of strategy or clear thinking, which leads to the death of Optimus Prime. Hot Rod is the main character of the movie and can transform into a sports car. At the end of the movie he is the one that Optimus talked about, and uses the power of the Matrix to light the Autobot's darkest hour by destroying Unicron and turning into Rodimus Prime.
He doesn't get to speak in the movie (he did have something to say in the original script though) Hound first appears helping Kup to set up the road block to Lookout mountain. Later on he is seen near Optimus' shuttle after it has landed, although he may have survived the battle at Autobot City and rolled out to greet Optimus. Which is what I like to think, anyway.
Only the back of Huffer can be clearly seen, he's in the same shot that Bluestreak is, mentioned above. Whilst this is the only time he appears in the movie, it's worth mentioning that he's dead by season 3, he apparently did get killed in the battle of Autobot City as in the episode "Dark Awakening" his name is listed among several other dead Autobots. Can't say I miss him.
Stationed up on Moonbase 1, Ironhide is one of the oldest Autobots and is desperate to see some action after getting fed up of just watching the Decepticons on Cybertron. Optimus Prime sends him on a mission to Autobot City on Earth to gather energon so they can start a full scale assault, but the shuttle Ironhide is in is attacked by Decepticons and Ironhide is destroyed by Megatron. Which is a great shame because Ironhide was a great character, but since his toy had no head there really was no surprise he got killed off in the movie. 
Jazz is another Autobot stationed on Moonbase 1, but like Cliffjumper, he doesn't get to do any fighting and thankfully this means he doesn't get killed. Like Cliffjumper, he is sucked into Unicron but is later rescued by Daniel and escapes from Unicron along with Rodimus Prime and the other Autobots.
Another really old Autobot is Kup, whilst he's new introduced in the movie, he's shown to be an old timer and has gotten through many battles. In the movie, he's mostly seen giving Hot Rod advice and trying to keep him out of trouble, although it backfires when he tries to make friends with the Sharkticons.
One of the most recognisable Autobots, Optimus Prime is the leader of the good guys and can transform into a truck. He and some other Autobots have set up bases on two of Cybertron's moons, and Optimus is in charge of Moonbase 1. But after he receives a distress signal from Autobot City on Earth, he travels there and battles his arch-enemy Megatron. Although he defeats Megatron, the wounds he receives in the right are fatal and he dies after passing the Matrix onto his friend Ultra Magnus.
Autobot scientist Perceptor was first seen in the second series of Transformers but he's still a major character in the movie. He's present at the battle of Autobot City and manages to survive it, and later takes to space in a shuttle along with some other Autobots. At the near end of the movie he is on the Junkion ship with Wreck-Gar and the other Junkions, which is crushed by Unicron and thrust out into space, but given that Perceptor is present in the last group shot of the Autobots he managed to survive this, too.
Prowl can transform into a police car and was one of the first Autobots seen in the cartoon series, and in the movie he is on the same shuttle as Ironhide as it heads to Autobot City on Earth. But Prowl's life is ended when the Decepticons attack the shuttle and Scavenger destroys Prowl with a single laser shot.
Another of Blaster's new cassette robots, Ramhorn transforms into a rhino and is seen taking on Ratbat in his single appearance in the movie.
Ratchet was the Autobot's chief medic and often helped repair other Autobots in the first two seasons of the cartoon. In the movie, Ratchet is on the same shuttle as Ironhide and is destroyed by Megatron after being shot several times, although he at least got to dual wield two laser pistols before going out.
Another of Blaster's cassette robots is Rewind, who is exactly the same as Eject but coloured black instead of blue. He takes on Ravage in his brief appearance in the movie.
When Hot Rod uses the Matrix, he is changed into Rodimus Prime, who is a larger version of Hot Rod with a slightly different face and a new transformation mode where he can transform into a truck rather than just a sports car. After throwing Galvatron out into space, Rodimus uses the Matrix to destroy Unicron and at the end of the movie, he assumes command of the Autobots and tells them they will head towards a new age of peace and happiness.
Slag is another one of the Dinobots, and can transform into a triceratops, which is the mode he spends most of the movie in. Like the other Dinobots featured in the movie, he doesn't get to do much other than follow Grimlock around (and get into an argument with him after narrowly avoiding falling into a spike pit), although he did manage to knock Devastator over by himself.
The stupidest member of the Dinobot team, Sludge's picture you see there was the hardest to get out of all the Autobots and the only interesting thing that happens to him in the movie is that Devastator punches him really hard.
Springer is an Autobot triple changer, which means that he has three different transformation modes, he can either be a robot, car or helicopter. Since he's a new character he's in the movie quite a lot, his main moment being when he has a short fight against Wreck-Gar on the planet of Junk.
And finally, the last of Blaster's new cassette robots is Steeljaw, who is the first cassette to be released upon the Decepticon cassettes. In the movie, Steeljaw attacks Rumble.
Sunstreaker first appears helping Kup set up the road block to Lookout mountain, but due to a continuity error he's later seen co-piloting a shuttle with Optimus Prime as they head to Autobot City. Because of this, Sunstreaker misses the battle entirely and it means he most likely survived the movie, although this is his last appearance in the US cartoons.
The final Dinobot is Swoop, who can transform into a 
Autobot Earth commander Ultra Magnus is one of Optimus Prime's closest friends and makes sure that everything runs smoothly at Autobot City. After the battle of Autobot City, Ultra Magnus is given the Matrix of leadership and becomes the new leader of the Autobots, only to be destroyed by the Sweeps on the planet of Junk later on. He's rebuilt however but by the end of the movie his short spell as Autobot leader is ended after the new Rodimus Prime takes control,
although that suits him just fine.
The only appearance Wheeljack makes in the movie is when we get a brief shot of his corpse, which was totally sucktacular because he was one of my favourite characters and it was actually Smokescreen who was suppose to be here, not Wheeljack, according to the storyboards. But, since he appears in Transformers Victory, Wheeljack fans can rejoice. Also, the Wheeljack in the movie is missing his shoulder cannon, so it's obvious that he must be a fake used to confuse the Decepticons. 
The Jar-Jar Binks of
Transformers, Wheelie shows up on Quintessa out of absolutely nowhere and is given no back story at all. He's a small orange robot who can transform into a car and always speaks in rhyme, his voice was provided by Frank Welker who did the voices of characters like Megatron and Soundwave. The only cool thing about Wheelie in the movie is that when he first appears, this slightly creepy music
Like Wheeljack, only Windcharger's corpse is seen in the movie, how he died is unclear. But when Arcee is dragging his body out of the way, you can still see his 
One of the two Decepticon triple changers featured in the movie, Astrotrain is the Decepticon's main form of transportation between Cybertron and Earth. He can either be a robot, train or space shuttle, but the mode we see the most of is his space shuttle mode which is used to take all of the Decepticons back from the battle at Autobot City to Cybertron. Astrotrain is also the robot who places the crown on Starscream's head at the coronation sequence.
The other Decepticon triple changer in the movie is Blitzwing, who can either be a robot, plane or tank. His key moment in the movie is when he almost destroys Hot Rod in his tank mode, but a last second move by Kup means he misses and ends up hitting one of his own team instead. Later on in the movie he is in the Decepticon leadership battle and tries to take on Soundwave, but is thwarted by Laserbeak and Ravage.
Leader of the Insecticons, Bombshell seems to have patched things up with Megatron over the years and he and the other Insecticons attack Autobot City with the other Decepticons. It doesn't work out for Bombshell though as he is blown out of the way by a missile, and is so battered by the end of the battle that he has to be carried back to Astrotrain. He is later thrown out into space but is found by Unicron who changes him into a new robot. 
Bonecrusher is one of the Constructicons, and is the one who has the idea of "survival of the fittest" when the Decepticons wonder how they can fairly get rid of some of the weight slowing down Astrotrain.
When Skywarp is thrown out into space, he is rebuilt into a new robot: Cyclonus. Cyclonus serves as Galvatron's right hand man and can transform into a purple space fighter, and manages to gun down Hot Rod's shuttle by himself. There's a lot of confusion to whether or not he speaks in the movie, but he does get two lines, it's just his voice sounds quite a bit different to what it's like in the third season.
The only gestalt robot seen in the movie is Devastator, who is made up of all six of the Constructicons. Devastator first appears when he attempts to batter down a large wall at the battle of Autobot City, but he is stopped after being blasted with several missiles. Later, he takes on the Dinobots and manages to beat three of them, but is smashed into a wall by Snarl. The last time he appears in the movie is in the Decepticon leadership battle scene.
The first of the "cone-heads", Dirge can transform into a jet and he doesn't say anything in the movie. He was due to get a line during the Decepticon leader battle scene but this was cut, although he's still listed with a voice actor in the credits.
Frenzy is one of Soundwave's cassette robots and is mostly identical to Rumble, but his colour scheme is red and black rather than purple. The movie marks the last appearance of him in the US series as he is never seen again, although he clearly survived the battle at Autobot City. He does show up again in the Japanese Headmasters series though. 
When Megatron is found in space by Unicron, he is upgraded into a new robot called Galvatron, who is the most powerful Decepticon ever seen and shows this by destroying Starscream straight away and retaking his place as leader of the Decepticons. Not wanting to be a slave to Unicron, Galvatron secretly plans to destroy him and steals the Matrix from the Autobots in an attempt to use it against Unicron, but he fails. At the end of the movie he is thrown out of Unicron and into space by Rodimus Prime.
Another Constructicon is Hook, who doesn't get to do much in the movie other than call Soundwave a "
Kickback is another one of the Insecticons, and his most memorable moment in the movie is the part where he gets badly hurt when Kup runs over his head, putting a large dent in it. He is thrown out of Astrotrain along with the other Insecticons and made into a Sweep by Unicron. 
Another of Soundwave's cassettes, Laserbeak is the first Decepticon seen in the movie, where he successfully manages to spy on the Autobots at Moonbase 1 and find out what they are planning. He's later seen again when the Decepticons fight each other over who should be the new leader.
Longhaul is another Constructicon who can transform into a dump truck, although this isn't seen in the movie as all the Constructicons stay in their robot modes whenever they appear.
Megatron is the leader of the Decepticons and he has led them to victory by taking over Cybertron. But, he wants to totally destroy the Autobots and creates a plan to destroy Autobot City on Earth. Megatron eventually gets into a fight with Optimus Prime and ends up being smashed off a ledge and is heavily damaged. He is later thrown out of Astrotrain by Starscream, but is found by Unicron. Megatron is then upgraded into a new robot called Galvatron.
Mixmaster is suppose to be the insane one of the Constructicons, but he never actually speaks in the movie. He does survive it though and later on he stands with the other Constructicons as Scrapper says that they should be the new Decepticon leaders. 
Another cone-head is Ramjet who is known for his liking to simply crash into things rather than shooting them in the second season. In the movie, he doesn't get to do much other than be a standard soldier and is part of the Decepticon group which attacks Autobot City. He survives this battle and is later seen at Starscream's coronation. 
The only new Decepticon in the movie who isn't made out of someone else, Ratbat is another of Soundwave's cassette robots and transforms from tape to bat. His only appearance in the movie is at the battle of Autobot City where he and three of Soundwave's other cassettes stop Blaster's transmission and attack Perceptor. Ratbat
is beaten off Perceptor when Ramhorn tackles him. 
Ravage is is one of Soundwave's cassettes, and transforms into a jaguar. He first appears in the movie when Soundwave sends some of his cassettes to stop Blaster from contacting Moonbase 1, and he gets into a fight with Eject. Later on in the movie he helps Soundwave out when the Decepticons fight over who should be the new leader by attacking Blitzwing with Laserbeak. 
Lets get wordy with Reflector. In season 2, he was phased out of the show as the animators and writers were actually told not to use him, but he has several cameo appearances in the movie. His first appearance is during a shot of the battle at Autobot City, but bizarrely he's been 
Another of Soundwave's cassettes, Rumble is another little robot like Frenzy, but he's coloured purple. He leads the attack on the Autobot's communications tower and manages to stop a transmission from being sent out, although they did this too late as Optimus Prime still found out about the Decepticon attack on Autobot City. Rumble is later seen knocking down Devastator when the Decepticons fight over who their new leader should be.
Another Constructicon is Scavenger, who doesn't say anything in the film, although famously he manages to destroy Prowl when the Decepticons attack the Autobot shuttle. With one shot.
Scrapper is the leader of the Constructicons and usually does all of the talking for them. At the battle of Autobot City, Scrapper and the other Constructicons transform into Devastator, who is later defeated by Slag. Later on Scrapper suggests that because they transform into the most powerful robot, they should be the new Decepticon leaders, although this view is not shared by Soundwave. 
When Thundercracker is thrown out into space, Unicron finds him and changes him into a new robot called Scourge, who can transform into some kind of air skiff thing and is in charge of the Sweeps, a bunch of Decepticons who happen to look just like him. Scourge only has one line to say in the movie, reminding Galvatron
that they "belong to him" (Unicron).
As usual, Shockwave is always left on Cybertron and doesn't get to do anything that exciting in the movie. Due to an animation error, he does appear in one shot of the battle at Autobot City, and much later on in the movie he tells all the Decepticons to scramble as Unicron attacks. He was supposed to die at that point but since his death scene was cut, this never happened, although the movie still marks the last official appearance of him in any G1 animated series. 
Shrapnel is the last Insecticon, and like the other two he gets badly damaged at the battle of Autobot City and is later thrown out into space and is changed into a Sweep by Unicron.
Skywarp looks a lot like Starscream but in my opinion has the best colour scheme of the bunch, and like the other seekers, he transforms into a jet. He's present at the battle of Autobot City but apparently was heavily damaged as he is one of the few Decepticons to be thrown into space, where he is changed by Unicron into a new, more powerful robot called Cyclonus.
One of Megatron's most loyal warriors, Soundwave is really remembered for being the robot with the funky voice, and the fact that he transformed into a cassette player. Soundwave is present at the battle of Autobot City and survives it, and is kind enough to take the battered body of Megatron back to Astrotrain, only to vote to boot out the injured later on. Whoops. He later fights the other Decepticons as they battle over who should be the new leader after Megatron's demise, but he didn't win and is last seen in the movie watching Starscream's coronation.
The ever traitorous Starscream is still plotting to dispose of Megatron, even though the Decepticons have finally managed to win back Cybertron. Starscream is seen at the battle of Autobot City and survives it, and later is the one to throw Megatron out into space so he can finally take his place as Decepticon leader. However, his leadership is short lived as just moments after being crowned, he is destroyed by Galvatron.
Thrust can transform into a red jet and doesn't get to do anything interesting in the movie, although he's the first guy to be rammed over by Optimus Prime at the battle of Autobot City. 
The final Decepticon jet to feature in this list is Thundercracker, who looks exactly the same as Starscream and Skywarp, but he has a blue colour scheme. Apparently damaged during the Decepticon assault on Autobot City, Thundercracker is thrown out of Astrotrain, but is turned into a more powerful robot called Scourge by Unicron. 
Allicons are the named coined for the Quintesson troops that attack Hot Rod and Kup after they tried to communicate with them, and they can transform into alligator like creatures. Interestingly, in the script for this scene, Sharkticons were suppose to be there but instead, these guys were used. They are never named in the movie or season 3, but in Dreamwave's 2004
Transformers "More
Than Meets The Eye" comic series, they are called Allicons which is the name most fans now go with.
Quintesson bailiffs are the ones who rush into Kranix's cell to take him out to be sentenced. What I always find strange is that these guys are never sent in to attack the Dinobots when they attack. 
Quintesson executioners are the ones which throw the switch which drops the platform a sentenced robot is standing on.
Only one Quintesson judge is shown in the movie, who seems to be in charge of all the Quintessons - an idea I wish they'd kept, because by season 3 there are loads of judges throughout the entire season. Anyway, the judges are the ones who have
five heads -Rage (pictured), 
Again, only one Quintesson Prosecutor in the movie, who is easily identifiable by his alien-like head. He's also the one that is crushed under a door by the Dinobots.
Sharkticons are the name for the main troops of the Quintesson army. Whilst they don't appear to have the ability to speak in the movie, they can at least understand orders and are used to devour any sentenced robots who fall into the Sharkticon pool. They are then beaten up by Hot Rod, Kup and the Dinobots and they eventually understand that they should go and attack their leaders instead, which they do, but by the next season they are back under Quintesson control.
Arblus is one of only two robots from the planet Lithone's entire population to escape from Unicron when he attacks the planet. He is later captured by the Quintessons, who drop him into a pool full of Sharkticons who devour him. 
The new human character introduced in the movie is Daniel Witwicky, who hangs around with the Autobots at Autobot City whilst his father is stationed on Moonbase 2. Due to the Autobots seemingly showing no concern at all for his safety, he follows them around during the battle and goes into dangerous situations, and for whatever reason Ultra Magnus lets him tag along when the Autobots head to Cybertron to see what happened to the Moonbases. Daniel does save his father, Jazz, Cliffjumper and Bumblebee from nasty deaths at the near end of the movie so he's not a complete waste of time.
The only other survivor of Unicron's attack on Lithone is Kranix, who blasts off in a ship with Arblus. They are both later captured by the Quintessons, and after briefly meeting Hot Rod and Kup and telling them about Unicron, he is sentenced and dropped into the Sharkticon pool and is eaten. 
The Autobots human friend Spike Witwicky
has now aged twenty years since we last saw him in the second season and is stationed on Moonbase 2 with Bumblebee. When Unicron attacks Moonbase 2 he and Bumblebee blast off in a ship and set off the bases' self destruct sequence, but this doesn't damage Unicron and their ship is sucked inside of him. Spike nearly dies but is saved by his son Daniel. 
Appearing out of nowhere, the planet sized Unicron is the main bad guy in the movie. His motives are unclear but his only weakness is the Autobot Matrix of Leadership, which he sends Galvatron to go and destroy. Unicron later transforms from his planet mode to his gigantic robot mode and attacks Cybertron, but he doesn't destroy it because he is blown apart when Rodimus Prime uses the power of the Matrix to destroy him.
Junkion leader Wreck-Gar seems to be a bit on the hasty side of things when he's introduced, as he leads the other Junkions to attack the Autobots for no real reason at all. It's all a misunderstanding though and soon the Junkions and Autobots are best of buddies, and he helps them to fight Unicron. Wreck-Gar and all of the other Junkions always talk with TV language they've picked up, and because they're made up of old parts they are experts at repairing things, including themselves.
