1. The Godfather
2. A Clockwork Orange
3. Schindler's List
Honorable Mentions:
Full Metal Jacket, The Silence of the Lambs, The Dark Knight, Raging Bull, V for Vendetta, Rocky, Superbad, Saving Private Ryan.
Really, anything by Stanley Kubrick is an instant favorite of mine. Best director in movie history. His work is incredible.