Pulling off the "swastika dancing" scene on-stage. One of the best moments in "Springtime for Hitler" is the above shot where you see the dancers in a swastika formation. They simulated this on-stage using a large mirror and mannequins on dollies... and it worked.
The original movie
In real life, Mel Brooks winning a Best Original Screenplay Academy Award for his very first movie screenplay. Also take into account how often comedies get Award Snubs on Oscar night, and how long it took The Producers to find its audience during its original theatrical release.
Leo finally grows a spine and says one of my favorite lines in the movie-musical-movie. "And you're right, Mr. Marks! You are a CPA! A certified public ASSHOLE!"
"Stop the world, I wanna get on!"
In the film, Nathan Lane keeps singing while he throws his hat in the air, opens a door, and catches it, all in one take.
The absolutely massive Tony sweep. Not even Mel expected that big of a victory.
The bum in the bar belting it out in a deleted scene. And said bum was played by Ernie Sabella.