I was listening to Storm radio earlier (the one who went for a license in Manchester - they've got a London based station that is on cable) and I must have heard a contender.
William Shatner sings (well, talks!) Common People by Pulp. Its a real cover and the DJ mentioned the little singing bit being by someone from the Datsuns or something. But it is a real Shatner song, all stuttering and out of tune and out of time! I recommend you listen to it once, if for nothing other than worried amusement