I saw "Carrie" the day it opened. I think I was 13 or 14 years old. To this day, I have not heard a sold-out audience scream quite like that collectively. The final shot was set up so well, too, with the "Summer's Eve douche ad" approach: tranquil pictures, soft focus, warm colors, and Pino Donaggio's lovely music, and then ... GOTCHA!!!
They tried it in other horror movies after that, like the end of Friday the 13th, and it worked, more or less.
I'll add a few others to my list:
The crucifix scene in The Exorcist
The pea soup fountain in The Exorcist
The final shot of the Blair Witch Project
The "big reveal" near the end of Don't Look Now
Mom in the rocking chair in Psycho
The shower scene in Psycho (well, maybe not the 350th time you've seen it, but try to remember back to the first, particularly if it hadn't been spoiled for you yet)
The reveal of Damien's "mother" in the grave, in The Omen
And of course, the entire film of A Chorus Line.
"Jaws is the Citizen Kane of movies."
blocked: logan2, Diamonds3, Hamilton22