I so suck at these. I'm a huge film fan, but I just can't call up titles off the top of my head. Lots of great titles listed. I always like any of the P.K. Dick treatments.
There's always some impressive **** in some really awful sci-fi films. I finally forced myself to watch Prometheus the other night. Ga! What a train wreck... but amidst that wreck, the usual amazing performance by Michael Fassbinder (is he ever bad in anything). He along with Tom Hardy look to be the type of actors I'm gonna end up enjoying in frickin anything.
Most of mine are on here. 12 Monkeys is probably my favorite.
Some of the ones I didn't see on here
Primer. It's an ultra small budget Sci-Fi film dealing with the power of having time travel. It is quite confusing in parts, but honestly it is an awesome film, especially for a movie made for under $10,000
I'm not quite sure if I wold call it "Science Fiction" but Pi is another great low-budget film that has some Sci-Fi elements.
I also liked AI, but thought the tacked on ending was stupid. I lost a bet with friends, when I bet that movie would gross $300M domestically. It eventually made it 1/4 of the there
Eternal Sunshine of the Spotless Mind - I'm genuinely surprised no one else has said this.