Some friends and I were discussing this the other day, as we were sitting around on a rainy afternoon, watching 50's era "flying saucer" movies. There seem to be films out there that have directly impacted the myths of UFOs in the years following the big "flap" of the late 1940's. The Day the Earth Stood Still had it's sleek "mound" spaceship, which no one could scratch, out of which came a ramp and doorway, only to disappear again... "Killers From Space" put Peter Graves through a classic 90's era abduction/probing/operation experience... "Earth Vs. The Flying Saucers" took a lot of it's details from the Donald Keyhoe book of the time, and added some hokum of their own... including the first look at what has since evolved into the EBE we are so familiar with today. EvsFS could also be considered a template for the Betty and Barney Hill reports of later years.
Can you think of any other examples of films which added to the "knowledge" we currently have about UFOs?