Looking for good recordings of female vocals I have not yet tried...

The quintessential female jazz singer is Peggy Lee. Check out the album The Ultimate Peggy Lee, it is recorded very well and her style is so unique and subtle while extremely effective. Songs she made popular, 'Why dont you do right' with Benny Goodman, 'Fever' in 1958. She wrote and produced , 'I don't know enough about you'.  Many more including the classic, 'Is that all there is'. Just a very under rated songstress from thr 40s and 50s. Many say she was the female version of Frank and I agree. Adding morr fuel to the fire they are reportedly to have hooked up frequently. Not surprising.

Cassandra Wilson and Norah Jones, both on Blue Note Records (and in audiophile pressings by Analogue Productions).

+1 (I'm partial to NJ's "Come Away With Me" and "The Fall").

+1 for Alison Krauss/US "Live".  Incredible recording and her voice is heaven-sent.

I might also suggest Patricia Barber.  Her recordings are well-engineered and she has one of those "smokey" jazz voices.  Not to mention some very wellp-written pieces.

Try Sophie Zelmani.  Specifically the track called 'All About You' on the Soul album.  You'll swear Sophie and the players are in the room with you.  And it's only Redbook CD quality.  I can only imagine how good a hirez version would sound.

You can also try Lake Street Dive's 'Obviously' album. Rachel Price is a very soulful vocalist and this album has some catchy and clever tunes.

Rachel, if you read this please get the Lake Street Dive posse down to S. Fla.

Eva Cassidy 'Live at Blues Alley' Proof positive She could sing any song, any genre, better than almost anyone. 

Emmy Lou Harris 'Spyboy' Maybe the best album she ever made.

Jewel 'Have A little Faith In Me' from the 'Phenomenon' soundtrack. She morphs into Janis Joplin halfway through the song as her band channels 'Big Brother & the Holding Company. Amazing. Totally worth finding.

Irene Kral accompanied by Alan Broadbent.