Not just in terms of voice, but impact; Tori Amos, Joni Mitchell, Indigo Girls, Eva Cassidy, off the top of my head...
At the moment 'Rites of Passage' by the Indigo Girls is a fave. 'Galileo', 'Ghost' and 'Love Will Come To You' are just fantastic songs, beautifully performed, lyrically interesting, satisfying, emotional. The first two mentioned are examples of songs with 'spooky chord sequences'; the very chords and changes evoke emotion. I've not bothered changing the CD in my car for a week, as I'd not listened to the album for ages...