Hard to argue with the choice of Aretha, but soulfulness takes a lot of different forms, and like Elizabeth said, it's not always easy to know why an artist touches us. Many good choices above. Here's another. This woman slays me:
Elis Regina
http://www.youtube.com/watch?v=35FPZR24djg&feature=related
Elis Regina
http://www.youtube.com/watch?v=35FPZR24djg&feature=related