As voted by the Guardian's expert panel:

1. Blade Runner
2. 2001: A Space Odyssey
3. Star Wars & The Empire Strikes Back
4. Alien
5. Solaris (1972, not the Clooney one)
6. Terminator & T2: Judgment Day
7. The Day The Earth Stood Still
8. War of the Worlds
9. The Matrix
10. Close Encounters of the 3rd Kind

Needless to say, I have some disagreement. I've never been THAT in love with Blade Runner, though it's pretty good I guess; it makes the list. I'd probably put 2001 at the top though. I would have had Aliens instead of Alien; it's the exact same movie, just superior. No Terminator for me; It's a movie, not a film (sorry, Ezra). I think 12 Monkeys deserves to be on there, as well as probably Brazil. Hell, I'd even consider putting Sleeper on there, because I love Woody Allen so much lately.

The original Planet of the Apes is absolutely on the list.

What else? The Sixth Sense? I was spoiled by a friend, so I never saw it at all, but all those other people seem to like it. A Clockwork Orange? I'd like to see a comic book movie up there: maybe the original Batman or Spiderman 2 or X-2. Throw those kids a bone for once. E.T.? No, I hate E.T.

A.I. and possibly even Minority Report make the list in the alternate universe where Stephen Spielberg doesn't ruin everything. Not in our universe, though.

And no Back to the Future/Back to the Future Part II? Come on, McFly! Back to the Future should be on there, and everybody knows it.

What else am I missing?

The trouble with this list seems to be a decision on the part of the Guardian to define science fiction so narrowly that basically only space opera qualifies. That's why I prefer "genre" or "speculative" or just "nerd" to "sci-fi", because then at least you can bring in movies that are mind-bending or bizarre or geek-centric (say, Being John Malkovich) without necessarily having laser guns.