Best Female Vocalists Ballads

Sinéad O'Connor is my choice and +1 to Melody Gardot.

I'll second Shirley Horn, and you can add "Cecile McLorin Salvant".

I am historically not a big Sinead O Conner fan but gotta say I always found her interesting and am almost always pleasantly surprised when I hear her stuff.

Same true for Milla Jojovich. "The Divine Comedy" is quite good. She did this when still quite young and demonstrated outstanding artistry and ability to present it. Whouda thunk it?

Second the suggestion of Vienna Teng -- be on the lookout for her live CD, "The Moment Always Vanishing", a great recreation of a small concert setting and a disc that rewards whatever improvements you make to your system