Emperor Palpatine, as a part of the Jar Jar generation I gotta say this guy beats Darth Vader by miles, gotta love Ian McDiarmid

Theodore "T-Bag" Bagwell, seriously, I want to rip his bloody head off each time I see him, stopped watching Prison Break now, but I can only hope he gets a slow painful death
Scar from the Lion King, seriously, who didn't cry when Mufasa died?
Then there is a whole row of people who generally classify as Anti Heroes.
edit: oh yeah.. and this:Frollo from Disney's Hunchback of Notre Dame. He killed innocent people, he enslaved a young man, he's an old man that lusted over young women, and he sings the most epic song ever sung.
Yeah, it's a cartoon, but it's a damn good movie. It's more for adults than kids anyway. I didn't even get it when I was a kid. Take out those three talking gargoyles and you've got a really badass movie.