Recommended female vocalists?

Looking for female vocalists w/ ultra soothing voices - something that could relax me at the end of a hard day.

To give a bit of reference my favorites are:

Sarah McLaughlin - Surfacing: I Love You, Do What You Have To Do, Angel, Full of Grace. Fumbling Towards Ecstacy: Wait, Good Enough, Elsewhere, Ice, Hold On, Ice Cream, Fear.

Enya
Everything.

Tori Amos
Entire Little Earthquakes album. Some of her other music tends to get on my nerves a bit, though.

I'm sure I'm missing out on a ton of artists. Who else do I need to check out? If it's not too much trouble please give specific albums and songs.

Thanks in advance.

-Kevin