John Podhoretz thinks it is 2001: A Space Odyssey, not that he could be bothered with a hyperlink.
Off the top of my head, here are a few better choices IMHO:
The Killing Fields (Seriously unfunny stuff)
Triumph of the Will (I hate Nazis)
Paths of Glory (A btter Kubrick choice)
Macbeth (The Roman Polanski version)
The Exorcist (Still the scariest movie ever)
1 the heart is the lonely hunter
2 in the bed room
3 saving private ryan
4 taxie driver // with bobby denero
5 the godfather 1 & 2