Equilibrium as someone mentioned earlier. Masterpiece right there with Christian Bale and other known actors.
Its a fanmade trailer as the original one sucks donkey dong
Most of the ones that I would have said have already been said.
just to throw in one more, a decent, non supernatural film is a french one called 'ils' or 'them' which is a nice example of your typical suspense horror.
Pandorum. Might not be extremely scary but it's a good movie with a strong cast nonetheless.
Silent Hill.
Really good, u wont be dissapointed.
Moon and Sunshine were the first two that came to mind.
Cube is also pretty good, I don't know if I'd necessarily call it sci fi though..
i don't really watch horrors, but i appreciate good sci-fi:
moon
sunshine
even horizon (those 3 were mentioned before)
2001: a space odyssey
2010 (space odyssey 2)
clockwork orange
blade runner
donnie darko
v for vendetta (not quite sci-fi, but still awesome)
planet of the apes (the original one, from 1968)
and i guess Solaris, but not because of film, because of book which was god damn awesome and film ruined the experience for me ;p
I have to say Firefly (xes its a Serie but its a short Serie) the best Sci-Fi Series out there and the Movie thats end the Series: serenity
And just for the sake that i love the Movie .... Plan 9: from outher Space !
aliens was awesome. only movies to scare the heck outta of me. saw that movie in theater and only movies to put me under theaters seats lol course i was like 10 or so at the time
scifi- Starship troopers (the first one, none of the others)
To be fair, there's really no reason 2001: a space odyssey couldn't count as a horror, it has all the characteristics of a horror film just in a sci-fi setting. Interesting movie to see such an accurate portrayal of space travel.. but the end was a bit much for me. Definitely a must see though.
I don't know if it counts as a sci-fi but the film version of A Scanner Darkly seemed pretty good to me even if the rotoscopic animation is a little.. bizarre. Warning: super serious movie