Some of the best of that genre include Solaris, Planet of the Apes, Alien, The Terminator, Blade Runner, A Space Odyssey, Metropolis, Star Trek, Star Wars, The Day the Earth Stood Still, and E.T.
It's a matter of opinion, so you may or may not agree but I think all the Alien movies, Predator, all the Terminator movies, Matrix and Star Wars are best.
DISTRICT 9 is a great science fiction movie. Humans discriminating extraterrestrials because they are different. The situation looks very similar to some real social issues in some part of the world.
This is of course due to some speculation. I would say the best around would be maybe the new avatar, donnie darko, Matrix, Star Wars and of course my favorite back to the future
Some of the best science fiction movies are the classics. I am talking about all of The Star Wars movies and others like The Matrix. There are other movies that have been put out recently that are good. I suggest Avatar if you have not already made a trip to go see it.