Most unusual/mesmerizing female voice.

Elizabeth, great call on Callas, was just going to add her glad you did.
Joan Sutherland early, early in her career what she could do with her voice, flexibility and strength, has yet to be equaled.

Kate Bush
Unusual? yup
Mesmerizing? see unusual

Yma Sumac, unusual, Dusty and Carly Simon mesmerizing plus Janis Joplin for being Janis Joplin.

Seconding Dodgealum on Jesse Sykes. Definitely some unnerving stuff on "Reckless Burning." Julie Miller on "Broken Things" a bit off the path too.

And yes, we do love Margo. :)

John

Billy Holiday in her prime.

I always liked the chick from Sixpence None The Richer also.

Beth Gibbons (Portishead) is another.

And lets not forget Eartha Kitt