What Is Your Favorite Movie Scene Of All Time??

From Parenthood, when Gil(Steve Martin)'s grandmother puts parenthood in perspective:

[Gil has been complaining about his complicated life; Grandma wanders into the room]
Grandma: You know, when I was nineteen, Grandpa took me on a roller coaster.
Gil: Oh?
Grandma: Up, down, up, down. Oh, what a ride!
Gil: What a great story.
Grandma: I always wanted to go again. You know, it was just so interesting to me that a ride could make me so frightened, so scared, so sick, so excited, and so thrilled all together! Some didn't like it. They went on the merry-go-round. That just goes around. Nothing. I like the roller coaster. You get more out of it.

But you left off the part that makes that scene wonderful instead of sappy:

(Paraphrasing from memory:)
"Then Grandma came along with her "roller coaster" story, and everything became clear!"
"Oh yeah? I happen to think your Grandma is BRILLIANT!!"
"If she's so brilliant, why is she sitting in our neighbor's car!?!"

I love the "Putting on the Ritz" scene from "Young Frankenstein." 100+ times and it still cracks me up.

The fencing scene from the Princess Bride ("I am not left-handed either!") and the follow-up ("There was a mighty duel...") and the next scene ("Someone has bested a giant!) and of course Vizzini ("Never get involved in a land war in Asia, but only slightly less well know is this: never go up against a Sicillian when *death* is on the line!) and finally "Hello, my name is Inigo Montoya. You killed my father. Prepare to die.) Or any other scene in that film.

The scene from "Eraserhead" when he has dinner with the in-laws. Put me off of fowl for months.

The scene in "Desperate Living"...yes, THAT scene (careful with those scissors!)

The scene in "Dune" when they first harness a sandworm...still visually stunning.

The opening scene to "Citizen Kane"....plus it was the first film to show ceilings! Mundane now, but quite the accomplishment then.

The opening one-shot scene of "Touch of Evil."

The ending scene of "French Kiss." It's all about Kevin Klein's hands. (He's married to Phoebe Cates, y'know.)

The scene in Kenneth Branagh's "Henry V" when he's professing his love for his future Queen Katherine, as well as Derek Jacobi's wonderful line delivery in everything, but espeially "Know you Fluellen?" and "....our play!"

Ben's death, and the subsequent closing sequence in "Night of the Living Dead."

Most of "Shawn of the Dead" especially "We're coming to get you Barbara!" and all the other Romero "inside jokes."

The first sight of the Monolith in "2001"

The rabid dog scene, the scene when Scout is told to stand because her daddy is a great man, the attack scene, and the scene where we first see Boo Radley, all in "To Kill a Mockingbird."

The opening scene of "Xanadu" and ending scene of "Grease" (kidding!)

The saddest scene (which involves dogs) from "the saddest movie ever (TM)"
"Amores Perros."

"Singing in the Rain" from "Singing in the Rain."

That's all I can think of right now.