Several online radio sites, like pandora.com or slacker.com, let you set up a station for a particular artist; they will then play songs by that artist and others deemed similar. I've found that a good way to hear new artists that are similar to artists I like.
My dads wife likes this sort of thing and she also listens to Cara Dylan and Norah Jones. (Personally I find the latter a bit dull but she does have a good voice).There's a lass called Adele who's pretty popular and Gabriella Cimli who you may also like.
You could have a listen to:-
Feist
Cat Power
Bat for Lashes
Florence and the Machine
Adele
Yeah Yeah Yeah's
Some might be a bit more lively than the Artists youve listed but still great female vocalists!
Give 'em a Whirl!
Many thanks - I'm off to check them out now though I've already tried Norah Jones and like China Doll I do find her a bit 'lacking'. As for the youtube link - I gotta agree Kate Souza has a rather fine voice, I'll be interested to see what else she' done and pandora.com etc are also next on my list of things to do. Many thanks again.
go back to the original source and check out some Dusty Springfield. I know this answer will have you all rolling your eyes, and I'm not being cheeky (I promise!), but she really was quite amazing. She's the inspiration to a lot of these new artists, who are carrying on her legacy.