who sang the acustic song at the end of tonights episode "do no harm" (March 12.2009)

The song was a cover of Oasis's "Wonderwall" sung par Ryan Adams.

As for right now, I don't know, but this website lists all of the songs in each episode, and it usually mises à jour a few hours after the episode airs. I reccomend waiting till tomorrow and check.
link

I hope that helps =D