My "favorites" list changes depending on the mood I'm in and the genre I'm interested in at the time, but here goes:

1. 8 1/2
2. Blue Velvet
3. The Bicycle Thief
4. Once upon a Time in the West
5. For a Few Dollars More
6. Fistful of Dynamite (a/k/a Duck, You Sucker)
7. Monty Python and the Holy Grail
8. tie - Waiting for Guffman/Best in Show
10. This is Spinal Tap
11. A Clockwork Orange
12. Touch of Evil
13. Planet of the Apes (original)
14. Sunset Blvd.
15. East of Eden
16. Baby Doll
17. Pulp Fiction
18. The Matrix
19. Fifth Element
20. The Player

On another day I can see dropping 18, 19 & 20 and adding Full Metal Jacket, High Fidelity, Twin Peaks Fire Walk with Me, Camille 2000 and/or Lost in Translation.