Anton Chigurh, from No Country for Old Men, was pretty much pure evil, though he did have kind of a twisted code of ethics. "Heads, or tails, it's the best I can do. Terrific movie!
I like Heath Ledger's portrayal of the Joker, in The Dark Knight. Not as much of a caricature as Nicholson's or definitely Cesar Romero's.
And finally, Hannibal Lecter. He's just creepy.