This is always an interesting topic.  As always a certain degree of opinion can determine what is influential.  For example, Birth of a Nation might be better known, but is it as influential as Intolerance in the long run?
1. Citizen Kane
2. Battleship Potemkin
3. Breathless
4. Psycho
5. Forty Second Street
6. The Apu Trilogy
7. Double Indemnity 
8. Seventh Seal
9. Rashomon
10. 8 1/2
11. Star Wars
12. The General
13. 2001
14. City Lights
15. Intolerance
16. Nanook of the North
17. Napoleon 
18. Passion of Joan of Arc
19. The Bicycle Thief
20. The Searchers
These are just a running list, off the top of my head, so don't castrate me because of an omition.