I totally have to agree with Ocha about Maleficent from Disney's Sleeping Beauty. That woman was hardcore bitch. Just because she wasn't invited to a party she shows up and and makes a HUGE drama show "You know what. You pissed me off, so I'm cursing your daughter to DIE, bitches!"
And then, when she captures the prince, she's all. "I'm not going to kill you. I'm going to let you sit here in my dungeon for a hundred years, pining away for your poor princess. THEN when you're on the brink of death, I'mma let you go free! :D"
Frollo. Fuckin' Frollo. He was well developed, had an excellent song, and I felt bad for him while still realizing that he was an utter monster.
Tyler Durden, from Fight Club. Too damn quotable to not like.
Ink, from Ink. Speaking of well developed villains, this guy is the epitome of it. In the film he's both a villain and a hero at the same time - you feel bad for him and hate him at the same time.