SecondHand Songs

If anyone else is a cover song junkie like myself, you should take a look at Second Hand Songs. It's a fun database that you can search by song, artist, and album. There is an advanced search too that you can use to specify relationships between songs, if the song was a tribute to someone, what label it appeared on and in what medium, etc. The site also provides you with interesting bits of trivia, such as:

California Dreamin' by Royal Gigolos was originally written by John Phillips, Michelle Phillips and performed by Barry McGuire in 1965.

(Everyone knows it's a Mamas and the Papas tune, but I didn't know my fave Barry McGuire covered the song!)

It doesn't seem to include live performances, but only those covers that have actually been recorded. You can also contribute to the database if you see any gaps.