This is a really cool idea. Say you love a song and want to know if someone else has done it? Maybe you hear a song that sounds incredibly familiar and you're just sure it must be a cover song. Maybe you love a band and would like to know if anyone has covered one of their songs or if they have done any covers of other bands. Or possibly you're in a band that wants to do a cover song that no one has already re-done.
Check out The Covers Project, a database of songs that have been re-recorded by other artists.