other singers like Patricia Barber.....


trying to find other female singers with similar style.
i've listened to Diana Krall, Cassandra Wilson, Jane Monheit, & Karrin Allyson. Karrin Allyson was good but the others were either too much fluff or too different.
Barber seems to be dark with an edge. i'm not a big fan of "happy" music which seemed to be Krall & Monheit.
lwatson
Try Dave's True Story. It is not precisely like Barber, but it is very, very good female vocals. Dave's True Story plays/sings very dark comedic music that is quite entertaining. Chesky records them.

see www.davestruestory.com

KF
Flora Purim, Cesaria Evora both from Brazil. Don't pay attention to Portugese if you don't understand. Just simply listen to their voices and music. Flora Purim sings English in "Light as a Feather" album of Chick Corea. You should definitely get her brilliant work with Dizzy Gillaspie "Rhythmstick".
If you want to hear a realy different female vocal in terms of theme and style try Sally Oldfield(UK). You should seek to find her participating in albums of Mike Oldfield, Pierre Moerlene or Pekka Pohjola.
Meridith Monk is on the highest sophistication level but you can give her a try -- maybe you'll "swallow it" maybe not.