Here's one most people have never heard. It was released in 2011, and included on a 2nd disc of the 'Wish You Were Here' Experience Edition. The normal version that most people have heard was sung by Roy Harper, after both Roger Waters and David Gilmour didn't think their vocals fit the song. So in this version, David Gilmour sings in the front, with Roger Waters singing at the same time in the back ground.
This one is an alternative version of 'Wish You Were Here', which was released on the same disc above. In this one,
Stéphane Grappelli was in the studio to record an album at the same Pink Floyd was recording this song, and he came in and started to play his violin on the spot.