The Mummy with Boris Karloff. It wasn't even necessary to watch the movie. The nightmares started just by watching the picture/movie still in TV-magazine.
The Thing from Antother World (1951) with James Arness as "The Thing". I was watching this film at the age of 9 or 10 together with my younger siblings under the watchful eyes of my grandmother. When the nightmares started the following night my parents had do deal with and it was my poor grandma who got a shydtload of complaints.
Concerning "The Mist": Watching the first time was like a load of sleeping pills. But years later I learned to appreciate the art of the movie and it became a little bit more scary.
