I remember the first time hearing Zee Avi's Honey Bee in a commercial and thinking (IIRC) that this song is so special, even being in a commercial can't diminish it. It's on a level all its own, like all classic & magical songs are. Edit: There's a chance that I'm completely imagining that I heard it in a commercial though.
The other ones that come to mind are a Pomplamoose tune, that "apple of my eye" tune, a few others that were in commercials but far above that level... I'll have to look them up.