Katherine McPhee is the 24 year old finalist of American Idol's Season 5 (ending May 2006) (links to idol and wikipedia pages)
On May 2, she sang what is now my fave performance from the show, "Black Horse and the Cherry Tree" which was originally sung by some singer called KT Tunstall
Youtube and Google Video are very religious about DRM so they won't let people upload the video. I found it on a new site here. There is also an audio mp3 recording here - let me know if any of these links are broken.