Some of my favorites:

John McCutcheon (especially the album "Fine Times at Our House", which I'm not sure is still available
Tim OBrien (one of his I listen to constantly is "Songs from the Mountains"
Jean Ritchie
Peggy Seeger
Mike seeger
Pete Seeger
Sally Rogers
Claudia schmidt (especially earlier stuff)
Lou and Peter Berryman (I have a twisted sense of humor.)
John Hartford (saw him live, and he fiddled, clogged, and called a dance all at once!)

None of these in any particular order, and certainly not an exhaustive list. :)

Teresa