I think Midge Ur's version of Man Who Sold the World is better, but it's a bit quibbly if that really counts as original artist David Bowie contributed to it.
Edit: MSI's cover of Supertramp's Logical Song song is a pretty good cover if you like MSI and not Supertramp. Similarly with their cover of Tom Sawyer and Rush respectively.
David Byrne covers Crystal Water's Gypsy Woman. I'm not sure it's a better cover, but it is unique in that I don't know any other cover of a dance track into not a dance track.
Well I'm sure the snakes don't call him a saint...