In the wake of the British government's fifth and largest release (6,000 pages) of UFO files, the Los Angeles Times wrote an interesting editorial on how the extra terrestrial crafts we see change shape based on what's en vogue in pop culture. For instance, in the '40s, flying saucers were the shape of sightings and correlated with those in films such as Forbidden Planet. Then the triangular shape took over in sightings around the same time audiences discovered the Star Destroyers in Star Wars (left).
Granted, some might say it's the aliens influencing pop culture and not vice versa, but who am I to say? I just think it's an interesting observation by the Times.