One of my favorites, maybe top, is Daniel Day Lewis as Bill Cutting.
He's just an all around badass. A ruthless early New York scumbag who chooses sharpened melee weapons over guns. He plays one of the best roles I think I've ever seen. The way people get boners over how Heath Ledger plays The Joker is how I feel about DDL as William Cutting.
His bad eye, big mustache, huge top hat on top of his greasy hair and his deep bone chillingly vicious voice make him one of the best characters in any movie.
This speech is great too:
The fact that he kills Amsterdam's (leo) father in the opening scene makes him the villian of the movie, but as it goes on, you see that even though Cutting is a no good bullying thief like everyone else, he really almost becomes a father figure to Amsterdam and it makes you sad when he gets
Spoilers!
killed.
There Will Be Blood was really good, but man I really don't know too much what the hell it was really about towards the end.