Other memorables:
The Graduate - The whole wedding scene when Benjamin runs to ceremony and screams for Elaine to stop, especially when he rips the cross off the wall and puts it into the door handle to lock the patrons inside the chapel. Even better than Mrs. Robinson's seduction earlier in the movie, if you ask me.
Lord of the Rings: The Two Towers - The whole Last March of the Ents scene. It is said that Tolkein was terribly grieved by the effects of the industrial revolution on the small farming village he grew up in. Watching the trees come alive and destroy the machines that would destroy the forest is great.
Requiem for a Dream - Who can forget Marion giving in and performing in the orgy party for a fix?
The Empire Strikes Back - As Han is being encased in carbonite:
Leia: I love you.
Han: I know.
What a pimp.
Once Upon a Time in the West - The end of the opening scene when Harmonica comes off of the train playing his song and confronts the three scoundrels.
Harmonica: Did you bring a horse for me?
Scoundrel: Looks like we're a horse shot.
Harmonica: You brought two too many.
Then he shoots and kills all three scoundrels.
The Godfather Part II - The closing scene where Michael is sitting in the lawn chair remembering a birthday party, with all of his brothers and parents still alive and happy. In all of his youthful idealism he announces to them that he is going off to fight in the war, a war that he returns from as a decorated hero. As he is remembering this, he is having his brother Fredo killed, completing his simultaneous rise to power and fall to darkness.
Revenge of the Sith - The intercut at the end with Padme giving birth and Anakin receiving his cybernetic coat of armor. Padme draws her last breath, insisting there is still good in him, as the helmeted Darth Vader draws his first breath. The rise of the completed cyborg, in that Frankenstein-like medical room, with Qui Gonn's funeral dirge playing (incidentally, Qui Gonn's funeral was where Anakin and Palpatine first met), is quite memorable. Heck, we've been waiting to see that for over twenty years, all of my life.
Dr. Strangelove - The war council scene where the doctor cannot control the tic in his arm, which keeps trying to shoot into a heil Hitler pose.
Chinatown - The ending where the whole incest thing is revealed. Jesus, that's weird, and very well-acted.
ET - Come on, who doesn't love the bicycle lifting off for flight? It's hackneyed at this point, but only because it was so memorable as to be endlessly copied and parodied.
The Matrix - When Neo and Trinity raid the military building to free Morpheus. It's a little diminished by its association with the trenchcoat mafia, but even so, the scene is absolutely dazzling.
Indiana Jones and the Last Crusade - I love the part when Donovan has just finished dissolving and the last knight of the round table says "he chose poorly."
All Quiet on the Western Front - The end scene, when Paul is sitting in the trench during the de facto cease fire after all of his schoolmates have been killed. He stands up to reach for a butterfly and is shot. Every single primary character introduced in the film has been killed off and the film ends.
This is Spinal Tap - I think this may have been a deleted scene, but they're at the zoo and Derek Smalls is commenting on gorillas: "As a race, gorillas like all kinds of bread, yet they've never developed any baking skills." Every scene in this film is hilarious.
Platoon - Elias' death scene is one of the best ever.
A Clockwork Orange - That scene with the giant dildo is unforgettable.
