The best performance dance scene (so just a straight performance, not part of the plot) is the Nicholas Brothers doing the Jumpin Jive scene from Stormy Weather. The bit where they jump over each other into splits on the stairs is completely insane.
https://youtu.be/_8yGGtVKrD8?si=1gvYxuSQOwTE1skZ
For a number that is part of the plot, I personally have to go with "Cool" from the 1961 West Side Story.
https://youtu.be/wugWGhItaQA?si=VMKvxhuQI_Ln8TYg
There are way, way too many to list. Pretty much any Fred Astaire solo, the finale of An American in Paris, Make Em Laugh from Singing In The Rain, Cell Block Tango from Chicago, I'm Just Ken is hilarious choreography.
And don't forget Bollywood classics like Chaiya Chaiya (the one on the train).