I couldn't help remembering Gene Kelly's appearance on the Muppet Show, where the muppets kept trying to get him to do the famous title scene from the film. I located the bit on YouTube (URL: http://www.youtube.com/watch?v=5NiF33BSWaM):
Edit: According to the Wikipedia article, Gene Kelly was born in my hometown of Pittsburgh PA, and worked at the Pittsburgh Playhouse, where I took acting classes and had my first paid job, playing piano, during high school. Cool!