exceptional voices of female singers (non-classical)

If you are talking about pure vocal magnificence, perfect timbre, and extraordinary range that is absolutely mesmerizing, then any compilation about this topic is a complete joke if these two are not included: Eydie Gorme and Linda Eder. Without a doubt, two of the finest, most spellbinding and  enrapturing voices ever. I've seen Linda Eder 3 times, and am in awe of her.  Eydie Gorme, of Steve & Eydie fame, died about 3 or 4 years ago. She sang in English and Spanish, and the power and clarity of her voice was incredible. I saw her in the early '80's with Steve Lawrence and she was astonishing.  She was a once in a lifetime talent. Go to Youtube and you'll see, all you young whippersnappers! The same can be said of Linda Eder (twice in lifetime?) Linda Eder is a national treasure who should be a huge star, but she doesn't seek the lime
light. She makes most all go these popular singers of the day sound like complete hacks. Ironically, she started out on Star Search in the 80's and blew everybody away, won easily and later had success on Broadway.  These two reign supreme if you are talking about "the instrument" in my opinion.
 Eva Cassidy is right up there also. Honorable mention I would say Peggy Lee, Ella Fitzgerald, Astrud Gilberto (the Girl from Ipanema), Streisand in her prime, Nancy Wilson, Dinah Washington, Julie Budd, Julie London, Karen Carpenter and I'll throw in Shelby Lynne because her "Just a little lovin'" album is a knockout.
Bottom line; excluding Eydie Gorme and Linda Eder from any list of greatest singers invalidates the whole discussion, imho.

Ella
Celine Rudolph
Maria Bethania
Beyonce
Whitney Houston
Trisha Yearwood

Should add that Celine Rudolph is German jazz singer based in France who has training in African and Brazilian music in addition to jazz. Check out her legant vocals on her album with remarkably talented jazz guitarist Lionel Louke titled Obsessions. The music is beautiful, intimate, and playful.

Maria Bethania is a singer, a mega-star, from Brazil; her music spans styles from samba to bossa nova to jazz. Check out Santa Barbara, the first track from her 2009 album Encanteria. Gorgeous vocals. Beautifully recorded.

G

Aziz Ali, Gillian Welch.......

Great question., most surveys by highly regarded voice coaches consider Karen Carpenter the finest contralto voice ever recorded. Just released complete set of new vinyl albums.  Feb 4 will be 35 years since she died.