As vmiaiet said, there are movies that are probably going to be talked about no matter what: The Sixth Sense and The Usual Suspects. I would also add Se7en.
The thing with plot twists and surprise endings is that they’re no longer surprising after the fact. So all you can do is remember the films that left you off-kilter and in shock and caused you to recommend the film to others for those same feelings. I’ve got four that come to mind:
I was very lucky to have never been spoiled on the ending. If you were like me, then you know exactly what I’m talking about. If you weren’t like me, then I think the question is, Did you still find the movie as suspenseful? Were you able to lose yourself in the moment?
2) The Spitfire Grill
I haven’t seen this movie since I was a little girl, but I remember how shocked I was by the tragic ending. It really made the movie, and it was the reason why I recommended it to people to watch for years.
3) He Loves Me, He Loves Me Not
Audrey Tautau was famous for her portrayal of the waifish protagonist in Amelie, and all her roles since then have capitalized on that image. This movie was like if Amelie had been told from the perspective of the guy. It seems like a simple, unimaginative story until that plot twist when the whole thing gets placed on its head. It’s creepy!
4) The Triplets of Belleville
This movie never happened the way I thought it would, which is its greatest charm. To guess the story is to do the impossible. To ponder the ending is to try to pull a Cassandra: No one would believe the truth. Every turn is a twist, and every twist is a turn. This is perhaps one of the most delightful movies I’ve ever watched, and the suspense is all in the most basic tenet of storytelling: What will happen next?
And now I’m also thinking about how shocked I was at the ending of Fight Club back in the day… .
Fun Fact: The first I’d ever heard of The Triplets of Belleville was on the show So You Think You Can Dance? So when I watched the movie, I kept looking out for the piece of music performed to by our contestants. Truly a fantastic surprise when it happened!