GoogleVideo has it online:
Earth vs. The Flying Saucers is probably best known for the special effects contributed by master craftsman Ray Harryhausen. This is the movie in which saucers demolish the flower of democracy's architecture.
Although overshadowed by this imagery, the film is quite solid on its own. It's full of 1950s standards, like splashy shots of plot-point-specific newspaper headlines and a Walter Winchellesque introduction, but it's got some original material as well. The plot twists slightly at a few junctures, and while they're not hairpin turns, they transform a plain movie into an interesting one.
1000 Misspent Hours says,
This movie’s creators set out to make a flick about aliens kicking human ass until they get their own asses kicked in return, and that— and nothing else— is precisely what they did. And for that very reason, or so it seems to me, this movie is one of the best beloved classics of 50’s science fiction.
Earth vs the Flying Saucers is almost an archetypal 1950s alien invasion film.
Part of the fun to be had with Earth vs the Flying Saucers is the inventivity that has gone into the script (which comes partly from prolific B-movie hack Curt Siodmak). It comes packed with all sorts of novel inventions and devices – forcefields, room-sized computers, a device that indexes all the information inside a human head, the aliens in their blank metal suits with helmets that are revealed to operate by amplifying the senses, rayguns and flashing Van Der Graaf accelerators, even a muddled suggestion of relativity theory at one point.