8. Ymir (Twenty Million Miles To Earth, 1957)
Following the commercial and critical success of the previous year's Earth vs the Flying Saucers, a substantial cornerstone in the 'alien invasion' genre- as well as the inspiration for Tim Burton's Mars Attacks!- Harryhausen saw no reason to leave outer space just yet. And so Twenty Million Miles to Earth tells the tale of a rocket that has crash-landed in Sicily on its return voyage from Venus. The ship is carrying the egg of an alien life force known as a Ymir (although, curiously, this name never crops up in the film) back to Earth for examination. Unfortunately, the Ymir grows into an enormous reptilian creature- complete with scales and long, sweeping tail- before promptly escaping from the laboratory and running amok. His rampage, scattering man and beast through a crowded zoo, is suddenly curtailed with a well-aimed bazooka. Fun fact: Harryhausen has an uncredited cameo in the film, playing the man feeding peanuts to the elephants in the zoo.