"Gentlemen! You can't fight in here! This is the war room!"
Well I can't think of the absolute BEST at this moment, so I'll just put down what comes to mind.
This is really goofy, but one of my favorite scenes ever is the "Moses Supposes" song in
Singin' in the Rain. Not so much the song itself, but the dancing in the instrumental part of that. It's so complicated and involved, and they make it look so effortless.
Also, the "Piano Duel" between 1900 and Jelly Roll Morton in
The Legend of 1900 is such a great scene. In that same movie, the scene where 1900 first meets the trumpet player, when they let the brakes go on the piano at night, and they're just gliding around the room with the great music, is a beautiful scene.
Another one of the most memorable scenes ever is the cremation scene in the original
Ocean's Eleven, when they all slowly look at each other when they hear the noise.
I don't want to give out any spoilers, so I'll leave it at that.
Also, a scene that always gives me goosebumps is towards the end of
Immortal Beloved, during the very first performance of the 9th Symphony. The entire symphony scene is beautiful, with the flashbacks and stuff. But the part I'm talking about is the end of it, when Beethoven gets up on stage, and after it's over, he doesn't even know that the audience is giving him a standing ovation because his back is turned. Actually, that whole silent part, where all you hear is his heartbeat, is really amazing.