"The Children": about a schoolbus full of kids that passes through a toxic cloud. Their fingernails turn black and they want to hug you... which causes you to melt! A stupid, terrible movie now, but totally horrifying as a kid.
"Night of the Living Dead" (1968 B&W version) gave me zombie invasion nightmares for three months straight!
"Alien" I saw in 2nd grade, and my dad took me out right after Brett died (I was watching through my fingers, my younger sister was under the seat cringing in terror). I had to buy the photo-novel and Heavy Metal Illustrated Version to find out what happened...
"The Nightwalker": William Castle film. Still creepy today.
"Willy Wonka": Oompa-Loompas were creepy!
"Bumble" The Abominable Snowman in that Rudolph the Red-Nosed Reindeer stop-motion animated Christmas special terrified me. Island of Lost Toys maybe?
The Patterson "Bigfoot" footage really freaked me out! I saw a Aliens/Loch Ness/Bigfoot/Abominable Snowman docu-movie (with recreations) when I was a kid... The Bigfoot recreation had a woman knitting in her living room while her husband was watching football. She heard strange noises and saw a giant shadow outside her window through the curtains, called her husband up to investigate, and when he opened the front door.... BAM! Bigfoot was standing there! I think it was implied he killed the entire family, but maybe that's my imagination. It really kept me up for nights, worried Bigfoot was gonna get me!
