Modern day female jazz recommendations

You need to check out Rachael Price that is mentioned
in Tabl10s's post.

A lot of good suggestions, I would add one name knowone has mentioned, a wonderful Scandinavian singer called Katrine Madsen. There really is a lot of good Jazz coming out of Scandinavia, perhaps it's the long dark winters. She does'nt have a large discography, but has an expressive, smoky contralto voice. I love Holly Cole, Karrin Allyson, Stacey Kent and others, but Katrine is my favourite. "You are so beautiful" is a great starting point, but all her CD's are strongly recommended, nothing on LP as far as I know.

Not Jazz you say, maybe technically but...If you're just looking at great sounding female vocalists with great music... K.D. Lang with Tony Bennet is awesome and rather Jazz based, There are a ton of Bonnie Raitt songs that are sheer vocal delights. Also, Michelle Shocked has a great voice. Another blast from the past, the Linda Ronstadt triple album, think it's called "After Midnight" recorded with the Nelson Riddle orchestra...INCREDIBLE! The Trio albums of Linda Ronstadt, Emylou Harris and Dolly Parton are pretty sweet too. As others have said, Patricia Barber, Eva Cassidy, are great, one smokey and sultry the other open clear and sweet.
But if you want fire and brimstone female vocals (not Jazz for sure) The all time queen is still Janis. No, not Ian,.... Joplin.

Definitely different Jazz singer and try the track Money to slap a bass!

Get the Pamela Brown CD with Horace Parlan.Her career mainly in Europe but she's great.Did I mention Stacey Kent before
Cheers
Chazz