Years ago we used to do Weille Waille (I'm deamned if I know how to spell it) with one chord. We had a guy in the band who couldn't play but he would pick up the guitar for that one song and someone would put his fingers in the right place and away he'd go. A lot of people thought he could play, which says something about how observant audiences can be. Another song that used one chord was Sonny and Cher's "The Beat Goes On". When I first played guitar we also played "Peter Gunn" with one chord though I'm sure there should be more.