Cassandra Wilson and Norah Jones, both on Blue Note Records (and in audiophile pressings by Analogue Productions).
+1 (I'm partial to NJ's "Come Away With Me" and "The Fall").
+1 for Alison Krauss/US "Live". Incredible recording and her voice is heaven-sent.
I might also suggest Patricia Barber. Her recordings are well-engineered and she has one of those "smokey" jazz voices. Not to mention some very wellp-written pieces.