exceptional voices of female singers (non-classical)

What I'm talking about here is what critics of classical singing refer to as "the instrument": the exceptional beauty or uniqueness of the timbre of the voice qua voice.  For the moment, put aside preferences w.r.t. repertoire, interpretation, performance, style, delivery, etc., and just consider the *sound* of the voice.  We're *not* talking about favorite female artists here, because that kind of preference is based on a whole amalgam of factors.

I suspect some of the top figures in the category I've tried to define often aren't very popular among audiophiles, because of those many other factors.

My first three nominations: Barbra Streisand, Linda Ronstadt, Eva Cassidy.

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Damn, how could I have left out Patsy Cline?! And Carole King?! And Big Mama Thornton (the female Howlin’ Wolf)?! Etta James, Eartha Kitt, Irma Thomas, Patti Page, and so many more.

Some of the same as mentioned by others and some I love I didn't see mentioned;

Sandy Denny
Alison Krauss
Laura Nyro
Dionne Warwick
Joni Mitchell
Anaïs Mitchell (No relation) Saw her live recently...unbelievable beauty in her voice, great songwriting/guitar and overall vibe, beautiful woman, inside and out;