Google just nods the massive cyber head and holds all its wisdom and points me to a message board where countless other mothers who have been forced to watch the Shrek movies thirteen trillion times have CAP-LOCKED that same question and someone else has answered them in a snarky and slightly condescending tone: (I'm paraphrasing)
"Obviously you live under a sound-proof rock, or you would have known that that song is 9 Crimes by Damien Rice and Lisa Hannigan....although I will stoop to share your frustration that whatever dumbass was in charge of putting together the soundtrack left out one of the best and most important songs in the movie."*sigh*
Thank you Google. And you, condescending musical guru. That song has been haunting me for about 5 years now.
SIDENOTE: That might be one of the weirdest music videos I've ever seen. Seriously. WTF? You'd think he'd take better care of his new floating head.