Ballad Makin' in the Mountains of Kentucky by Jean Thomas, and Jean Richie's Singing Family of the Cumberlands are both worth a look.
Would echo Joe's inclusion of the filk - Songcatcher, very loosely based around Sharp's co-author Olive Dame Campbell - good fun with some superb singing, though some people did take umbridge at the depiction of Sharp as a latter-day Mr Toad.
Jim Carroll