It's called "Breathe Me" by Sia. Interesting choice for the series finale. RightClickSaveAs and pretend you're Claire driving down the highway:
Sia - "Breathe Me" (MP3 Link Expired)
Bonus:
Sia - "Breathe Me (Mylo Remix)" (MP3 Link Expired)
Four Tet, Ulrich Schnauss, and Mr. Dan also have remixes worth searching out.
