Impossible to pick a favourite, it's almost endless. If Pushed, off the top of my head I would certainly include the following : Bajka, Bjork, Hope Sandoval, Mary Gauthier, all of the Be Good Tanya's, Dolly Parton, Savina Yannatou, Oumou Sangare, Sally Nyolo, Souad Massi, Sainkho Namtchylak...