A couple of more names for your list:
- Brand new (CD just released this week) - Diane Birch "Bible Belt"
- Tracy Chapman - distinctive folk-rock voice
- Karrin Allyson - jazz influences
- Suzanne Vega - good alterative sound
- Fiona Apple - another alt singer
- Erin Bode - think of a jazz/pop Alison Krauss with Dido phrasing- start with "The Little Garden
- Anna Nalick "Wreck of the Day" - another very recent release. If you like Dido, you'll like her.
Plenty more but this and the others is a good starter list.