Rope
Absolutely thrilling! I loved everything about it, from the one-room setting to the camera work, down to the phenomenal acting. The way the tension slowly but steadily mounts and builds up creates a perfect crescendo. It also poses a very interesting intellectual and moral debate, and Jimmy Stewart's final monologue is the cherry on top to end the movie.
This might be my favorite Hitchcock movie, and that says a lot considering Hitchcock’s legendary filmography.