I don't know, to me Science-Fiction is anything that takes existing technology and either uses it for something it can't currently be used for, or advancing it to a a large extent. Unfortunately, under this defintion would include everything from Blade Runner to 24 (Chloe, use your satellite to get real-time updates on any place in the world in 0.5 seconds!). That's why I'm limiting my list to movies in which this advancement-to-technology aspect is, if not a main theme, then at least exceedingly prevalent.
As for Star Wars, by the way, I consider it Sci-Fi/Fantasy, as I think it would be hard to argue that ther are sci-fi elements and fantastical elements. No one can argue that
all of the techonology used is completely implausible (or are we excluding any movies that have space ships, too?), so I'm including it in my list, as there is a prevelant science fiction theme pervading the universe.
- Close Encounters of the Third Kind - My favorite movie ever, so of course it's at the top here.
- Star Wars: The Empire Strikes Back - There's nothing quite like hearing Darth Vader say, "No, Luke - I am your father!"
- Jurassic Park - This one was a no-brainer. Excellent dinosaurs, excellent action, and based on an excellent book. What else do you want in your sci-fi movie?
- Invasion of the Body Snatchers (1956) - Still pretty creepy despite being more than a few years old, this is one awesome sci-fi movie that's managed to stand the test of time.
- Aliens - James Cameron did the only thing you could do with a sequel to Alien: he made it an action movie. And what glorious action it is.
- Star Wars: A New Hope - If you have to ask why this is an awesome sci-fi movie, why are you making a list?
- The Prestige - One of my absolute favorite films from last year, this is engrossing, as well as being able to pull off cloning in a period piece. How do they do it? I have no idea, but I'm so very glad they did.
- Alien - Very scary (especially the first time you see it), this movie is almost as good as its sequl in terms of sheer entertainment value (almost).
- 28 Weeks Later - Probably the least "sci-fi-y" movie on my list, but the central conceit involves a made-up virus that was manufactured in a lab, so it counts for me. Very good action, and very good zombie effects, and just an all-around awesome movie.
- Blade Runner - Blade Runner is awesome. You will agree.