I've long been a fan of Ben Folds, and have seen him a couple times live, and he's consistently great. He's also got a great sense of humor, and even worked with the great Improv Everywhere for a hilarious live show prank--a "fake" Ben Folds.
Recently, someone who looks and sounds just like Folds has been Piano improv-ing on Chatroulette under the name "Merton".
(This is a newly edited and reposted version--the original I posted here was taken down, and "merton" edited it to appease YouTube...)
Though Folds is apparently still denying he is Merton, he recently did an "Ode to Merton" at a couple live shows, and the results are pretty amazing: