other singers like Patricia Barber.....

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.

These are all excellent and creditable responses, but for my money, there's no one who's truly *like* Patricia Barber. She's one of a kind, and may we have her around for many more decades to come.

I realy forgot about Angelique Kidjo. Such exotic voice of voices!

Holly Cole. She has Jane Monheit's technical skills with Patricia Barber's dark, powerful interpretation. Good stuff. Start with Temptation (all Tom Waits covers).

If you want to explore an unknown novelty, bordering on off topic, try Bet Williams at http://www.epiphanyrecords.com/. She's more a kind of arty singer songwriter than jazz/torch song singer, and I can't vouch for the recording quality, but you could check out some mp3s at the site. I would tend towards "Epiphany Project" (Bet Williams & John Hodian) than the album with "Ooh La La". That latter song is not my cup of tea. Try "Lockerbie" and "Long Gray Line".