I have a very limited selection:
~The taxi cab scene in On the Waterfront. That scene shows very clearly how Marlon Brando got an Oscar for that movie.
~The New Year's scene in The Godfather Part II. Just thinking about it sends chills down my back.
~Shark shows up in Jaws. Anybody that's seen that scene probably vowed never to go swimming at the beach again. EVER.
~The "mad as hell" speech in Network. Just watch that scene and you'll see how Peter Finch got that posthumous Oscar.
~Bluto smashing the guitar in Animal House. The fact that he apologizes makes it even funnier.
~The opening scene of Manhattan. The images are just beautiful.
Those are mine. What are yours?