Here's a site that offers people the chance to watch science fiction films online: The Classic Science Fiction Channel . It will feature actual films or offer links to sites (like Hulu TV) that offer these films for viewing.
Some of the films, like A Boy and His Dog and Metropolis are true classics of the genre. Others, like The Ape and At The Earth's Core are guilty pleasures carried along more by the cast and director than artistic merit. And still others, like Killers From Space and Voyage To The Planet of Prehistoric Women are just plain bad.
You can also get to view the ORIGINAL The Day The Earth Stood Still from 1951 as well. Check it out if you're considering going to see the upcoming remake with Keanu Reeves and see if it still holds up! -Ed