I second Joe on our own Judy Cook. Just last night I led a group to learn "My God He Is A Rock" just the way I learned to love it from her, and it was a blast. She has inspired me to sing (well, belt!), and every time I hear her sing, I find a fascinating song or story I have to get to the bottom of, and learn a little more 'folk' and a lot more history!

http://judycook.net/demo.htm

Dani