Young Frankenstein finds its Crowning Moment when Frederick, alone with the Creature, first panics - then finds his senses and tells the monster how wonderful it is. As he comforts his now-crying creation, his revived passion to show the world what he - they - have and will accomplish builds and builds, and he finally embraces his heritage:
Inga: Dr. Fronk-on-steen! Are you all right?
Frederick:My name is FRANKENSTEIN!
Igor's best moment is an unforgettable scene that took forever to shoot as the production crew couldn't stop laughing. Frankenstein, Igor and Inga meet Elizabeth as she arrives at the castle:
Frederick: Igor, would you give me a hand with the bags (luggage)?
Igor, imitating Groucho Marx: Certainly. You take the blonde and I'll take the one in the turban! (bites Elizabeth's mink scarf)
The Monster's Shaming the Mob speech after gaining intelligence, with Peter Boyle throwing an effective dramatic performance right in the middle of all the goofiness.
"PUTTING ON THE RIITZZZ!" *stomp stomp*
On the subject of that scene, consider the muscle control and memory needed to perform a song and dance routine such as that. Sure it might not seem it, but the monster earlier could hardly walk and only make groaning sounds. To learn to move and sing as much as he did, not to mention memorize it all, shows that he can do pretty well even with an "Abby Normal" brain.