If it's the girl with the long red hair and the slow motion, the song is called "Swamp" by Midwest Product (Album: A World Series of Love). I love the song from that commercial and thankfully, they (Hummer) were thoughtful enough to put that info on their site.... just go to www.hummer.com and at the bottom there's a link for "the new TV spot"... and there are stills of each commericial so you can click on each one and get all the info. sweet!
:)