JAWS, overlooked as horror, but it is.
Saw it as a preteen in the theaters first run. That night every time I fell asleep I dreamt that the shark would come sliding in my bedroom window. After about 5 or 6 times of that I turned on the light and read West Side Story in its entirety.
The cool thing about that movie was as a preteen, the girl in the row ahead of me. a teenager, was so scared that she held my hand over the back of the seat the entire movie. I thought I was THE MAN after the movie, my buddies not so much!
And going back to the OP, The Ring scared the crap out of me. Watched it alone in my theater in total darkness. Towards the end I told myself that if the phone rang I would just run out of the house. Then the menu pops up after the movie with the choice of "Do not watch this"...really!
When the movie (The Ring) was in the theater, they would wait till the movie was well underway,then they would bring out a tall ladder and lean it up against the wall. When the people came out of the movie they would freak out and run out the door.
The Ring 2, one of the worst movies ever.
One of the most disturbing endings to a movie ever was the remake of The Mist! Holy crap! Everybody in the theater was having a good time with typical King material, very much crowd participation. Then the ending scene happened and everyone walked out in utter silence.
Night of the Living Dead, still freaks me out every time, cant sleep after, it wont let me.