There’s another scene, in which Salieri is showing the Emperor a march he’s written (and which he’s quite proud of). Mozart comes in, demonstrates that he can play the thing after having only heard it the one time, and then says, “It’s a little simple, isn’t it?” And then he utterly transforms it.
Yankee Doodle Dandy–When George M. Cohan meets Eddie Foy.
Duck Soup–The mirror scene
1776–When it all comes down to James Wilson’s vote, and John Dickinson’s reaction.
The Two Towers–The Battle of Helm’s Deep
Spider-Man 2–“Got any more bright ideas?” “A few, yeah!”
Singing in the Rain–“Moses Supposes”
Beauty and the Beast–(Disney version) The ballroom scene
The Princess Bride–“I’m not left-handed either.”
The Little Mermaid (Disney)–“There’s just one problem left.”
When James Cagney tap-dances his way out of the White House in Yankee Doodle Dandy.
When the WWI vets perform “Oh, How I Hate to Get Up in the Morning!” in This Is the Army.
Mrs Robinson tries to seduce Benjamin in The Graduate.
“What color are their uniforms?” in The Good, the Bad, and the Ugly.
Tuco buys a pistol in The Good, the Bad, and the Ugly.
Bond fights Grant in From Russia, with Love and Oddjob in Goldfinger.
From A Shot in the Dark:
*“In both cases, the room was locked from the inside. In both cases, the only two people in the room were Maria Gambrelli and the murder victim. In both cases, Maria Gambrelli was found standing over the murder victim holding the murder weapon in her hand. What is the obvious conclusion?”
“Maria Gambrelli is guilty.”
“You FOOL! Can’t you see she is PROTECTING someone?”*
From Patton:
“You tell the General that I don’t care to drink with any Russian son of a bitch!”
Radl’s meeting with Himmler in The Eagle Has Landed. Donald Pleasance has always been a greatly underappreciated actor, IMHO.
Reidenschneider’s soliloquy in prison about witness testimony at trial and how people’s memories can be manipulated, in The Man Who Wasn’t There: “Looking at something changes it. They call it the 'Uncertainty Principle.”
Addison Dewitt confronts Eve in her hotel room about her past and blackmails her, in All About Eve.
The Dude’s highly referential drug dream after Jackie Treehorn slips him a mickey in The Big Lebowski.
The crooks arguing and bumping each other off one by one in The Ladykillers (the Ealing Studios one!).
John Wayne’s silhouette framed in the door, and he decides not to go in, at the end of The Searchers.
Nicolas Cage’s misfiling/alphabet scene in Vampire’s Kiss:
The Shining - “Here’s Johnny” Scene
Shawshank - When they warden remove’s Andy’s poster
Rear Window - The camera flash scene
Everyone has to see this scene in In Bruges. It’s one minute long and brings me joy every time I see it.
[“Why don’t you all just put your guns away?”
“Don’t be stupid. This is the shootout.”]("In Bruges" - Shootout - YouTube)
When Wallace is put to death in Braveheart
Mike Meyers playing his character’s dad ragging on the kid in So I Married an Axe Murderer
Al Pacino blowing up at Kevin Spacey in Glengarry Glen Ross
Jim Carrey running off the jetway in Dumb and Dumber
That was a wonderful, beautiful little movie. And yeah, great scene.
Two more:
JFK - ‘Back, and to the left. Back, and to the left. Back, and to the left…’
13 days: 'This is language!"
You have meddled with the primal forces of nature, Mr. Beale, and I won’t have it.
The “amateur night”/coffee cup ambush scene in Ronin.
The poisoned tea switch scene in Confessions of a Dangerous Mind.
The Mouth of Sauron scene from the Extended Edition of Return of the King.
The "You never go ‘full retard’" scene in Tropic Thunder.
The "Is this your pen?" scene from Casino.
The "life’s little Twinkie gauge" scene in Zombieland.
The final scene in Inglorious Basterds.
The opening fight scene from The Rundown.
When the Ents go to war in LOTR - The Two Towers.
That was my all time favorite part of the book. When I saw it come to life on the big screen, well… I cried… I actually cried. No dialogue, just music, enraged Ents, and 150 nerds in the movie theatre applauding with me. It was epic. 
The cabinet meeting where they cut out the in the federal budget in 5 minutes in “Dave” to fund a children’s welfare program.
I love scenes like this that are accomplished with no special effects at all.
Another example: the original 1951 version of The Thing, when they discover the flying saucer hidden under the ice. No SFX at all; they just spread out to find the edges of the buried object, and then they realize that they’re standing in a circle.
My favorite scene in Galaxy Quest is the one in which Alexander Dane(as Dr. Lazarus, played by Alan Rickman) recites that line he hates to the dying Thermian Quillek. The love and wonder that shows in Quillek’s face, then he dies. Then Rickman goes postal on the alien who shot him.
Hey, Dad, you wanna have a catch?
Also, the helicopter scene in “The Matrix,” slightly beats out the Lobby Scene in the same movie.
Galaxy Quest is the best Star Trek movie ever made. 
(…And The Incredibles is the best Fantastic Four movie ever made.)