In the "Muscular Beaver" episodes of The Angry Beavers, Norbert's alter ego switched between good and evil every time he was featured. Originally known as "Baron Bad Beaver," he incorporated his side switches into his name, so in his third appearance he was "Baron Once Bad Then Good Now Bad Again Beaver." It eventually culminated with "Once Bad Then Good Then Bad Again and now something thats Neither."
Transformers has had a few such characters. In particular, it's hard to remember whether Armada Starscream was working for or against Megatron when he died.
Dinobot in Beast Wars betrayed the Predacons in the Pilot Episode when he realizes that Megatron did not bring them to Earth. However, in season 2, when he realizes that Megatron DID bring them to Earth, realizing that Megatron is smart after all and could win the Beast Wars, he flips back to the Predacons, only to come back to the Maximals at the end of the same episode when Megatron tries to force him to kill Rattrap.
The beast Era had a couple based on this: Blackarachnia and Silverbolt. Both were originally maximal protoforms who were found by Predacons. Silverbolt betrayed the Predacons and joined the Maximals after finding out who were the good guys. Then he convinced Blackarachnia to join them. In Beast Machines they go to Cybertron after the Beast Wars are over, Silverbolt is captured by Megatron and turned into the Vehicon general Jetstorm and Blackarachnia has to free him and brings him back. Then in the comics they are captured by Unicron and Blackarachnia gets infected by a virus which makes her evil again. Then after the universe war Silverbolt brings her back to their home dimension to turn her back again.
Wreck-Gar of Transformers Animated switches from neutral to criminal to Autobot to good for only one thing - GARBAGE! to Decepticon. This is as a result of his decisively screwed-up mind, which meant that he basically did whatever somebody else suggested him to do. At the end of the episode, Ratchet advises him to simply be who he wants to be, at which he promptly announces "I am Wreck-Gar! I am a hero!", and sticks with it.
The Constructicons don't really seem to understand the fact that the Autobots and Decepticons are opposing sides of a WAR THAT WILL DECIDE THE FATE OF AN ENTIRE PLANET, so they have a tendancy to flip between the two sides without a second thought. After jumping from Autobot to Decepticon for the first time, they still address the Autobots as friends and casually explain their reasoning, expecting the Autobots to understand (they did it because Megatron's oil tasted better than theirs). They flip sides about 7 times over the course of the series.
In the comics, which continue the series' plot, Xanatos is housing the gargoyles at his home again, all the while doing jobs for the Illuminati, who are becoming the new main antagonists. In other words, he's uninstalled the revolving door and started outright living in the threshold.
Macbeth was an interesting case. After his first encounter with the Gargoyles, Macbeth never went out of his way to attack them. They either were getting in the middle of his schemes (like finding Merlin's scrolls, which turned out to just be diaries) or was under mind control. During the World Tour, Macbeth parted on perfectly fine terms without trading blows, and is briefly seen supporting the gargoyles in a TV interview during the Goliath Chronicles.
In Filmations Ghostbusters, there were three mischievous imps called the Tooth Scaries, who really couldn't make their minds up; as one henchman to the Big Bad told them in one episode, "You don't know whether you want to be good or bad!"
Avatar: The Last Airbender: Zuko found himself constantly switching sides due to his confused feelings and lack of resolve. Halfway through the third season, he finally made up his mind, but even before that he was trying to save Aang half the time, mostly for his own selfish purposes. Lampshaded in one episode when no one takes his Heel-Face Turn seriously, and he accidentally burns Toph.
Man Ray from Spongebob Squarepants is a villain the first time we meet him. However, he's been fitted with a tickle beltthat tickles him whenever he does something bad. He finally tricks SpongeBob and Patrick into taking it off him before going on a rampage. However, whenever he's about to do something evil he feels the tickle of the belt, eventually prompting him to become a good citizen. It seems though that the belt's influence wears off after a while because in his next appearance, he's become a villain again.
Jack Spicer teamed up with the Monks more than once, sometimes as a matter of mutual benefits in taking down a common enemy, but once even as a genuine attempt to join the side of good. However, in the end he betrayed them once again and returned to evil, because he was afraid he'd be even worse at being a good guy than he was at being a villain.
The Yin-Yang World switches the alignment of anyone who leaves it without both the Yin Yo-Yo and the Yang Yo-Yo. Due to this mechanic, anyone can be a Heel Face Revolving Door.
Raimundo as well- he had one instance of switching because he wasn't appreciated enough, one instance of being possessed after doing something stupid, and another instance of switching because he wasn't appreciated enough, though this turns out to be subterfuge.
A common character type in kids cartoon shows, especially in the 80s, was the one obnoxious member of the regular cast who could be counted upon to do something stupid, selfish, and/or rude and act contrary to the interests of the group whenever the plot focused on their everyday lives, but was considered just one of the gang when the plot focused on the world outside the main characters. They'll be trying to get the other characters expelled from school just to win an essay contest one week, then heading to the amusement park with the gang like nothing happened the next. Examples include Junior on The Snorks, Brainy on The Smurfs, Bianca on Beverly Hills Teens, Eric on Dungeons & Dragons, and Reggie on The Archie Show. Modern versions on non-kids shows would include Cartman on South Park and Stewie on Family Guy.
Diaspro was never a nice person, and even good might be stretching it, but at first she was merely a jerk in the wrong place and ended up victimized. Come season 3 and she brainwashes Sky into loving her, resulting in her banishment. She returns in season 5 apparently reformed, and while she tries to break up Bloom and Sky she does nothing evil and is ultimately looking out for Sky's safety. Then in season 6 she teams up with the Trix in an attempt to assassinate Bloom, putting her squarely on the evil side once again.
Nebula was once a good fairy in the past, but her imprisonment by the Wizards of the Black Circle left her bitter to humans. She was one of the strongest advocators of committing genocide on them. When Bloom beats her she reluctantly stops trying to kill humans and is willing to forgive the wizards that sealed her. Then the wizards betray them, and she launches a coup on her queen in order to hunt the wizards down without resistance, planning to later resume eliminating the humans. Once the wizards are defeated, she regrets her actions and is forgiven, placing her permanently on the good side.
El Tigre suffers from this. Due to the influence of having a heroic father and a villainous grandfather, Manny's moral compass is always spinning. This is most evident when put in the herometer, a device that tells whether or not its subject is a hero. The readout flip-flopped between good and evil so much that it quickly exploded.
Shere Khan from Talespin is a Deconstruction of Ambition Is Evil, and as such shows that while a desire for only money and power (his self-proclaimed motive) is not necessarily a good thing, neither does it just make you a bad guy all the time. This means that in some episodes he's ruthlessly conspiring with sky pirates to create a fuel shortage and a monopoly, while in others he saves the day at the end by shutting down his corrupt underlings in their scheming plans, not because they were corrupt, but because they were holding the Idiot Ball a little too much and that's bad for business. He's very nearly a prototypical David Xanatos, with more of an emphasis on money rather than power.
Bender from Futurama embodies this far too often to list every instance, so here's two examples: In an episode where he lost use of his body, he became a musician and inspired thousands of broken robots, only to turn it into a scam when he recovered (and didn't tell anyone). In another episode, he and Fry join the military just so they can get military discounts, but when an actual war happens, Bender ends up throwing himself on top of an explosive to protect his fellows without a second thought, knowing full well that the blast will probably kill him. Generally speaking he's a Magnificent Bastard, but he's occasionally shown that there are some things he actually cares about more than his own selfish ends.
Butters from South Park oftentimes seems to end up working with Cartman on whatever his latest scheme is. Given Butters personality, however, it's more likely he just doesn't understand what he's doing.
Cartman himself has been through the door a few times. While usually a villain of some sort, there are times when he's treated as no more than just a jerk, rather than a person capable of mass murder. There are also times when his goals are almost selfless or his goals align with the 'heroes' of the episode enough that he's effectively the Big Damn Hero.
The Duke of Detroit on Motorcity. He's a bit of a Friendly Enemy or Anti-Villain, who's usually not as much of a threat to the Burners as Kane, but still opposes Mike Chilton at times. He's just more about having fun. He teams up with Kane in the first part of the finale, but is back to help the Burners in the second part, carrying out this trope.
Discord of My Little Pony: Friendship Is Magic. His premier had him as a full heel. He turned partially face in season 3 thanks to Fluttershy, turned heel again at the end of season 4, but turned full face at the end of that episode.