The eponymous Beast from Disney's Beauty and the Beast. He starts out seeming like the monster he appears to be, but we soon learn the anguish he feels about this behavior and how it's prevented him from becoming normal again (he even has a song about it in the Broadway version). His interaction with Belle then steadily pushes him into the realm of a Jerk with a Heart of Gold.
The DVD commentary discusses it in great detail, citing that no matter how bad he is your sympathy must always be with the Beast in order for the movie to work, and thus a lot of emphasis is given the constant emotional pain he lives in.
The eponymous protagonist of Coraline starts off the movie being essentially a self-centered brat, although, arguably, she does have a Freudian Excuse in her distracted parents. She also goes through a lot of heart-wrenching crap: Having to deal with the Other Mother wanting to eat her and keep her for herself and wanting to sew buttons on her eyes as well as nearly losing her parents and losing the Other Father and Other Wybie.
Nuka, however qualifies. His father chooses an unrelated cub over him, he's portrayed as The Unfavourite to his mother, and seems to be the Butt Monkey of Zira's pride. While he does want power, he also wants to gain the favor and attention of Zira, who is more concerned with Kovu. In the end, he dies trying to prove himself to his mother, and even fails at that. He spends his last breath apologizing to Zira for failing, his death prompting one of the only displays of love and affection that Zira probably ever showed him.
Tigress as well, at least in the second half of the movie.
Depending on your interpretation of him and his Freudian Excuse, Lord Shen of the second movie. Considered too weak and sickly to warrant his parents' attention, Shen was left to the care of the Soothsayer. He strove to earn his parents' approval and ended up discovering the explosive potential behind fireworks. When the Soothsayer foretold his defeat at the hands of a warrior of black and white if he continued down his dark path, Shen slayed the pandas, believing averting his fate would finally earn his parents affection. They instead banished him and Shen saw this as the final sign that his parents did not and would never love him. He spends the rest of the movie killing and destroying out of a desperate need to fill the void in his life, knowing full well there is nothing he can do to make himself happy but also knowing there is nothing he can do to justify his actions.
Up: Charles Muntz - rejected by the scientific community, eluded by a stupid bird for sixty years, all by himself, going completely insane...it's so tragic...Of course, murdering innocent people because he thought they would take his bird away makes him a bit of a monster.
Shrek: Prince Charming. After enduring grief and humiliation now that he no longer has the power his mama gave him, all he wanted was his own Happily Ever After... which he probably would have gotten had he not stayed a villain by choice.
Perfect Blue: Rumi. She ends up delusional and tries to kill Mima. Me-Mania too. Yes, he was a serial killer and attempted rapist... But that's because he was a deformed, barely-functioning schizophrenic who lived only for his perfect image of Mima. The scene where we see his apartment is an enormous Stalker Shrine and that all he wants in life is "the real Mima's" affection was genuinely sad.
The eponymous character of Megamind. On one hand, he's an Ineffectual Sympathetic Villain who regularly kidnaps Roxanne, threatens citizens with bodily harm and always tries to kill his nemesis, Metro Man. On the other hand, he lost his entire civilization to a black hole, he grew up in prison because the inmates took advantage of his genius and naivete, and was ostracized in school by the kids because. unlike Metro Man, he looks different.
Princess Atta from A Bugs Life. She's rather strict towards her own younger sister, Dot. Not to mention refusing to see Flik's inventions as a good thing to help the ant colony. But she is rather nervous about her problems with taking over as a Queen that you're amazed she doesn't go further.
The ant colony itself as a whole. Sure, they brought the Darkest Hour on themselves by ostracizing Flik and PT Flea's entire circus after they hear the truth about the "warriors". But do they deserve the treatment Hopper gave to them afterwards?
Dave from Penguins of Madagascar. Once living at the Central Park Zoo, he had a roomy habitat and all the fans. Then started a chain where penguins unintentionally stole his glory as the octopus was moved to zoos and aquariums around the world, where he was forced to live in small tanks.
Prince Hans from Frozen. See his backstory for details and motivations of his actions. (i.e. growing up in a loveless family).
King Haggard from The Last Unicorn. The man was captured every living unicorn in the world and plans to harm our protagonist (and his own son!), but one can't help but feel sorry for his motivation: he's never been happy in all his life, and the only thing that ever gave him joy was the sight of unicorns. Anyone dealing with depression can surely understand, when your only source of happiness is one specific thing, and how that can make one act obsessive.
Lampwick and the other Stupid Little Boys in Pinocchio are a bunch of punks who enjoy destroying property, fighting, smoking, and drinking, but their ultimate fate ( being transformed into donkeys and sold into slavery) is far beyond what they deserve.