Ahh, some good movies listed here!

Barbarella - a young scantily clad Jane Fonda was the best part of that flick.

Soylent Green is awesome; then you'll have to check out the other Charlton Heston sci fi movies: The Planet of the Apes (origionals of course).

David Bowie was in a wacked out scifi movie in the 70's 'the man who fell to earth'.

'Logan's Run' is awesome.

'Dark City' was really great and not what you'd expect at all.

'Contact' with Jodie Foster.

What was the movie with O. J. Simpson were they faked a Mars mission?

'Sky Captain and the world of tomorrow' was an astounding movie.

'Galaxy Quest' was amusing.

'The computer wore tennis shoes'

'The Black hole'

'Escape from Witch Mountain'

'Flight of the Navigator'

'Outland' - Sean Connery?

Both great movies. I loved them as a kid.

However, my absolute favorite Sci-Fi right now is a series, not a movie. Only 14 episodes. Although there is a movie coming out in September.
You need to buy FireFly! Of course, it's more about the character's than SciFi. The movie will be called Serenity, which is the name of their ship.

... I'm sorry, what?!

My i second the recommmendations of Gattaca, Contact, Logan's Run, Fifth Element, Pitch Black and Chronicles of Rid.d.i.c.k. (stupid censorship) Excellent movies. But stay away from Paycheck, it might sound good but it's not.

How could you forget Cherry 2000, that movie is awesome!

Don't believe to him if you want to see a great serious science-fiction movie. If you want some kiddish fantasy movie then go for 'Space Balls' or something like that.

I would suggest also 'Red planet', it's a pretty good one.

Warning: Don't, I repeat DON'T see "Mission to Mars" ..the horror.. the horror..

Oh, I dunno. It had rather good special effects for its time (though it's still not bad). good acting (Jodie Foster, Tom Skerrit, and James Woods.. come on people!), a good musical score, and a very good story which I didn't really find preachy at all.. almost the opposite in fact.

[spoiler]
In fact, it's almost anti-faith with as much as Ellie, the main character, is constantly stepped on and over because of government politics and her (lack of) faith.
[/spoiler]

The end is a good couter-balance to that, though without going overbord.. and as far as I'm concerned does a commendable job at making the viewer think. Movies that are able to do that are quite rare these days.

The movie as a whole was also quite down to earth, so it is what you'd actually term science-fiction, instead of science-fantasy. I definitely recommend it.

Sky Captain and World of Tomorrow is a movie that came out in October or November. As for Science Fiction movies:

Matrix
Matrix Revisited
Animatrix
Matrix Reloaded
Matrix Revolution
Lost in Space (kind of kiddie but it has Mimi Rogers:))
Barbarella
Outland
Star Wars
Star Trek movies
Dark City
Fortress
Fortress 2 (both of these star Christopher Lambert)
Resident Evil
Resident Evil 2 (released Tuesday here)
Highlander movies

There is also a few that I have that have them classified as horror sci-fi on the back of their cases:

Leprechaun(I have the entire seies)
Friday the 13th(the latter movie cases classified this as horror/sci-fi)
Nightmare on Elm Street/Wes Craven's New Nightmare(WCNN was h/sci-fi also)

Note: In my opinion all Christopher Lambert movies are good. Not all of them are sci-fi, though, cause his movie Gideon was a great movie IMHO and it wasn't sci-fi at all.

I liked Contact as well. And Matrix... only the first one.

I can't not second this movie... the Matrix (One! The good one!) killer.

Dark City, Equilibrium, Paycheck, Minority Report, Final Fantasy, Impostor,...

EDIT: Futurama

A second for Minority Report.