If "horror" means "scary" then The Day the Earth Stood Still gets my vote though it's really science fiction,. All I know is that it scared the shit out of me. I first saw it on television around the time of the Cuban missile crisis when it looked to my twelve-year-old eyes like we were going to wipe each other off the map any day. So along comes this seemingly invincible guy from another planet who tells us that if, by chance, we don't destroy our planet they'll destroy it for us if we start shooting our little bombs into outer space. Gee, thanks!