This list consists of pure science fiction films with no superhero films. That falls under a different category. I know people will say that horror and sci-fi sometimes overlap, and that is true as do other genre's, but the film has to be more science fiction than any other genre for it to be considered a true science fiction film, and these are the top 25 best and must see films.
Honorable Mentions Not on the List: The Book of Eli, Source Code, Star Trek (2009), I am Legend, Terminator 3: Rise of the Machines, Minority Report, Pitch Black, Twelve Monkeys, Jurassic Park, Predator and Brazil.
http://m.ranker.com/list/25-greatest-science-fiction-films-of-all-time/miragerules, anything, star wars, science fiction, scifi, SciFi and Fantasy, other, star trek,
2001: A Space Odyssey
2010: The Year We Make Contact
Alien
A Clockwork Orange
Dark City
Fahrenheit 451
The Thing
Star Wars Episode V: The Empire Strikes Back
The Andromeda Strain
The Day the Earth Stood Still