I love the Diabelli Variations. I hope you're not going to spoil it for all of us! (I bet Leonard Bernstein did a lecture about it - I should go looking. Or maybe Andre Previn. They loved talking about that kind of stuff.)

For musical jokes, Bernstein talked about one of the Beethoven symphonies ending and ending and ending - I don't remember which now. It's probably all on YouTube.

And the Hoffnung Concerts were recorded and are still pretty wonderful.