I don't know if this thread is great because it's so interesting and there are so many great tips, or bad because I can just see my wallet bleeding!
Anyway, my two cents worth in no order:
Natalie Merchant - particularly her first two solo albums, and her life album (check out The Gulf of Araby - a beautiful track)
Beth Orton - Stolen Car is one of my favourite songs ever
Sarah McLaughlin - it would be a serious challenge to find a fault with Angel, one of the sweetest tracks ever
... and purely because of her contribution to REM's Shiny Happy People, Kate Pierson from The B52s.
Oh, and I remember that my dad was a big Anne Murray fan, so there's one for him (although I've never listened to her myself).