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

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. 

Can't believe nobody mentioned the Welsh witch, Stevie Nicks...with or without Fleetwood Mac.