Derek and the Dominoes cover of Hendrix's Little Wing...
The first thread I ever posted on the old boards was comparing John Mayer's "Free Fallin" to the original, after the doofi had shown me the cover. Little did I know, they had gotten Mayer's version from a previous thread a couple of days before. I was ridiculed mercilessly.
I think there's a solid argument that SRV's version is better than Hendrix's.