Mary Gauthier is another tremendous singer/songwriter along this line. I suppose technically her voice would be called an alto, although it's a bit more polished--and in better shape--than Lucinda Williams' tobacco-and-whiskey phrasing. Her Wikipedia page is interesting--apparently she's lived quite the life (and didn't write her first song till she was 35!).
My favorite song of hers is actually the roots-rocker "It Ain't the Wind, It's the Rain." However, looking over her website, I saw this video set to a montage of images from "Battlestar Galactica," about Lee Adama of all people, and couldn't resist.
If you haven't watched "Battlestar Galactica" (the aughts version, not the 70's "Star Wars" ripoff with feathered haircuts), you should do so immediately, of course. In the meantime, enjoy this mashup, and thrill to Mary Gauthier's wonderfully evocative voice.