Oops. What I meant to say was Julie Murphy, and Billie Holliday. And Linda Ronstadt, she had a great voice. And me Ma, obviously. Almeida Riddle! And Elizabeth Cotten. And Mahalia Jackson. And Beth Gibbons and Tracy Thorn from Everything But the Girl.
I always loved Sheila Stewart's voice, she has amazing gravity and gravitas. Can't think of anyone else. Or can, but too many.
cheers,
e c

(ps thanks john...;) )