Love those classic tracks. I find when I'm jamming I usually throw on those raw ones as it's easier to carve out your own voice when you're only up against a tinny acoustical track/vocals.
Some more!
Eva Cassidy - known more for her Somewhere Over the Rainbow cover, and similar ballads, she has an amazing blues repertoire, and one of the best voices ever to back it up.
Jim Croce is all swagger
Muddy Waters
Ray Charles