Songtitle.Info  is a regularly updated list of music used in television commercials (U.S. broadcasts). Around 1,000 songs from commercials going back to 1996. Most recent update -- Spring/Summer 2005. Most of the songs are linked to a clip at Amazon so you can check if it's the song you're looking for.
And, if you want to look for song lyrics, check out the tips at How to Find Song Lyrics Online .