Cool thread; a lot of good movies so far.

My five:

1) The Godfather

2) The Good, the Bad and the Ugly

3) On the Waterfront

4) A Clockwork Orange

5) Star Wars

Honorable mention:

Little Caesar
If you've never seen or heard of this flick you should really give it a look (I think it's coming out on DVD on Jan. 25th). It was made in 1930, so the sound sucks and the movie is kind of cheesy, but Edward G. Robinson gives the all time best performance in a gangster film, hands down. Everybody imitated him after this movie, from Bugs Bunny all the way up to Chief Wiggum on the Simpsons.