My top ten:

1. 2001 A Space Odyssey
2. The Matrix
3. Serenity
4. Planet of the Apes (NOT the remake)
5. Star Wars (either 4,5 or 6 - can't decide)
6. War of the Worlds (NOT the remake!)
7. Close Encounters of the Third Kind
8. The Day the Earth Stood Still
9. Fahrenheit 451
10. Star Trek IV: The Voyage Home