I know her personal life has been going down the toilet of late (and showing no sign of stopping the decline), but hearing Amy Winehouse on Back to Black was a revelation. Only heard the album late last year after seeing all the bad press and the terrible live apperances she did as my other half was raving about the album.
The woman sure has talent that's for sure, but I don't know if she can come back from the sad mess she's in.
Not quite what the OP asked for, but right now I'm listening to the sweetest voice I've heard in a long while: Christa Belle, from the band "Hungry Lucy". Try the album "Glo", "To Kill A King" is also supposed to be good. Very lush/syrupy.
over the rhine
a fine frenzy
I'd like to add:
Chrissie Hynde (check out the awesome acoustic live cd: Pretenders - Isle of View)
Malia (beautiful cover of Radiohead's "No Surprises" on the Young Bones cd)
Karin Bergquist / Over The Rhine (Almost everything she sings, but I especially love the Ohio cd)