I did too, slaw. I also neglected a favorite from the 80's, Maria KcKee of Lone Justice. Another unique, mildly "quirky" voice belongs to a little-known singer named Julianna Raye. Her Jeff Lynne-produced Something Peculiar album is fantastic! I met her in 2001, and was she surprised I knew of her! A very sweet, humble talent. I fell in love with her instantly.
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.