Here is a link to the Supernatural Music Guide on Supernatural.TV link
It has Seasons 1-4 and lists the music played in each episode. I think the S4 list is incomplete but I'm sure they'll finish it eventually.
My favorite ones in the show are
carry on my wayward son-Kansas (all seasons)
You Shook Me-AC/DC (Season 4)
Lonely Is The Night-Billy Squire (Season 4)
In A Gadda La Vida- Iron Butterfly (Season 1 haha
old I know but I love that song)
Crystal Ship-The Doors (Season 2)
And none of these songs could be played with out the Metallicar.