First off: great topic
Second: Someone mentioned the Hyperion Cantos books by Simmons - totally agree, some of the best sci-fi stuff out there (I was so disapointed to learn Scorcese dropped the movie project). Most Dan Simmons books are amazing and very well thought out. A must read.
More authors: Phillip K. Dick (anything he wrote), Kurt Vonnegut (Slaughterhouse 5 is genius) and the father of cyberpunk, William Gibson (i suggest Neuromancer).
Movies that were not already listed:
Black Hole (surprisingly good disney film)
Enemy Mine (not great but a good film still)
Dark Star (first Carpenter movie, and his best - a story of intergalactic garbage men)
Casshern (Jap anime style, real actors, quite eipc, relatively low budget)
Dune (David Lynch + sci-fi = wow.. but I didn't read the books, some say he ruined it all)
Alien 3 (not as bad as they say... and directed by Fincher)
Predator (first one with Arghnold)
Dark City (not great, but some good concepts, and Proyas still had some momentum from The Crow... then he lost his touch... iRobots was horrible, Asimov deserved better).
Captain Sky and the World of Tomorrow (for the style, little substance)
Post apocalyptic movies:
The Road Warrior (first one)
The Road (don't watch if you are on anti-depressants)
A boy and his dog (a good watch)
City of Lost Children (totally amazing, but originally a french movie. Maybe the translation killed it. It's the same Director as Amelie...and Alien 4; he can do the best and the worst and this movie is him at his best)
Delicatessen (same as above, same director: Jeunet)
For the laughs:
Spaceballs
Transmorphers
Bukaroo Banzai and the creatures from the 6th dimension
That's all i can think of off the top of my head!
Cheers,
PS - ... that's gonna be the best sci-fi flick in the last 20 years... long live Scott Free!
http://www.youtube.com/watch?v=sftuxbvGwiU