Ok, I had to have a good look through my collection, and found that I owned surprisingly little, however in order:
i) Timi Yuro - any of her early 60s recordings (Never heard of her? Neither had I until about 5/6 years ago, but believe me I reckon that she is head and shoulders above anyone else - she is hard to describe in terms of genre but interestingly Elvis apparently referred to her as his favourite female vocalist, though don't let that put you off).
ii) Melody Gardot [My one and only Thrill]
iii) Dusty Springfield [Dusty in Memphis]
iv) Sade [Diamond Life]
v) Janis Joplin [Cheap Thrills]
I am slightly surprised at the lack of soul singers, Aretha excepted.