When I was little, two movies genuinely scared and upset me. The first was Poltergeist). In particular, the scene where the tree) runs amok in the unfinished swimming pool. Also the clown doll.
However, Poltergeist doesn't hold up well. First of all, TV doesn't go off the air anymore, and second, I'm no longer afraid of claymation. Third: Coach.
The second film was one I, until recently, did not remember the name. I called it, at the time, "Monster Girl." I had reoccurring nightmares about Monster Girl for years. Monster Girl was scary. She had a messed up face and voice; she was very strong. She tried to kill her mom with a bureau. She could move things with her mind. And she swore. A lot.
Turns out, this film was "The Exorcist." And it holds up very well, in spite of it being released in 1973. It's got all the trappings of a typical 70's film, it's grainy, under-lit, and plods through the plot, but overall, it's well written, acted, and creates a genuinely terrifying picture that explores the boundaries of motherly love, faith, and medical bureaucracy .
Of all those things, the third frightens me the most. Medical Bureaucracy is terrifying, but that's a conversation for another time. Also, if you can enjoy some A+ quality profanity, it's well worth watching. Overall, it's Hollywood silliness and doesn't make a lot of demonological sense, but it's well worth watching again, especially if you can turn the sound way, way up.
Both the Exorcist and Poltergeist have had a strong influence on the American zeitgeist, both contributing iconic imagery that has been parodied many, many times. Both films are allegedly cursed. But only the Exorcist holds up as genuinely terrifying.