One of my favorites would be... I think it was the 8th episode of GTO. They busted out a Doraemon referrence, then switched over to a Kenshiro tribute, complete with action style. I literally had my drink come out of my nose when Onizuka pulled out a pen after smashing bowling balls, then grabbing a pen and saying "I'm not Doraemon, I'm Kenshiro!#%" and drawing on his chest while throwing people about. Has to be one of the funniest things I've seen in anime.

I also liked about 2/3s of Excel Saga.