You already know who Stephen Colbert is. But have you heard of David Ippolito? He's "That Guitar Man from Central Park." He's a barefoot (sometimes bare chested) guitar playing singer, and he's apparently got quite a following. I first heard of him on The Thom Hartmann Show, singing "Tom Cruise Scares Me," which also took on Dick Cheney and Ann Coulter.
This video teams him up with Colbert (OK, probably not).