If you like the more cerebral stuff (such as 2001 and Contact, which you listed) then you may want to check out Sunshine, even though the third act falls apart somewhat. The DVD/Blu also has a fine commentary with scientist and that film's consultant Brian Cox.
The Man from Earth is low budget (and it shows) but features several Trek cast alumni and was written by Jerome Bixby, who also wrote for TOS. It's talky and lacks action but if you like The Twilight Zone, you should enjoy this.
There's also A Scanner Darkly, which might be the most faithful Philip K. Dick adaptation. George Lucas's debut, THX-1138, is pretty thought provoking (or head scratching) but worth the time investment. It's two commentaries are also great listens.
Solaris is mentioned above. I'd recommend both the original Russian and the modern American films adapted from Lem's novel. Slaughterhouse Five, adapted from the Vonnegut novel, is pretty good, too. From around the same era you can check out Truffaut's hit and miss adaptation of Fahrenheit 451.
Primer, which like many of these titles is on Netflix, is probably the most complex time travel story on film. I've seen it three times and much as I think I understand it, I'm not sure I do!
I'd also second others who mentioned Moon, Dark City, Blade Runner, Gattaca, Children of Men, 12 Monkeys, Brazil.
On the other end of the spectrum, if you haven't seen it yet, check out Galaxy Quest (or as I call it, Star Trek V: The Intentionally Funny Frontier). And The Iron Giant is quite good, retro science fiction.