There are some great movies listed by some of the members here. Let me add:

The Fifth Element
2001: A Space Odyssey
Fahrenheit 451
Invasion of the Body Snatchers (the original, not the remake)
Invaders from Mars (1953 original)
1984 (George Orwell novel adaption)

and a great one because it is so BAD it comes off corny and actually funny: Plan 9 from Outer Space