For me, there is only one movie that ever scared the cr@p out of me....
from Amazon....
Jimmy Hunt plays the quintessential American boy of the post-war years--a freckle-faced kid named David who's curious, alert, and possibly prone to elaborate flights of fancy. Then, during a midnight thunderstorm, he witnesses the landing of a flying saucer that buries itself underground in a nearby field. David's father (Leif Erickson) indulges his son's urging to investigate... and thus begins a bizarre and chilling story of alien invasion, with David's cries of "Martians!" falling on deaf ears as more and more adults are abducted, probed, and placed under alien control.
Totally creeped me out. The only film ever to give me nightmares.
Feel free to add your own films.