What are your top 3 favorite female singers?

Merry Clayton who features on the Stones Gimme Shelter.

From Wiki,

Summoned from bed around midnight by Nitzsche, Clayton – about four months pregnant – made her recording with just a few takes and then returned home to bed. It remains the most prominent contribution to a Rolling Stones track by a female vocalist

* Aimee Mann

* Sarah McLachlan

* Ann Wilson

Joni Mitchell - "Blue"
Diana Krall - anything
Susana Baca - "Eco de Sombras"
Rosemary Clooney - "Do You Miss New York"

Ok, that's four.  But then I like Sade a lot too... 

I don't think anyone is overlooking anyone. The OP says 3. In another thread, I listed many many more. 

Many great singers listed here, I would add Carry Newcomer