I've shaken hands with and talked to Arturo Sandoval and Wynton Marsalis (both pretty famous trumpet players, especially Wynton). I saw Buzz Aldrin speak once, and almost but didn't quite shake his hand.

I had Jennifer Casolo as my GSI for a class. You may not know her name, but she was the focus of a bit of an international incident, apparently. She's on wikipedia (http://en.wikipedia.org/wiki/Jennifer_Casolo). Also, I've seen Robert Reich (Clinton's secretary of labor) speak several times, but that one doesn't quite count...he's a professor here.