There are far too many. Some played themselves such as McCartney. Some almost played themselves such as Michael Jackson and some played characters, Sara Gilbert (Darlene from Roseanne). You coul list them but it would take forever. The Who were a surprise one as was James Lipton from Actors Studio fame. One of the most long running ones is Kelsey Grammer (Frazier) as Sideshow Bob. Did you know that the guy who played Lionel Hutz and Troy McLure (Phil Hartman) was murdered by his wife 6 years ago and those characters have not figured since?