Although she's already been mentioned, I strongly suggest Ani DiFranco. I know squat about guitars... tried a couple times to learn, and it's just too much for me to coordinate one motion with one hand, and another motion with the other. (incidentally, I suck on the piano, as well... whoda thunk? Just give me my nice, simple clarinet, please... )
But... aaaaanyway, even my untrained ear can pick up the intricacies of her playing. A friend of mine, a guitar player himself, is immensely impressed by her, and believe me, he's not the type to go for angry-political-feminist folk rock.
Her first self-named album- just her and an acoustic guitar.
'Living in Clip'- a two-disc live set (incidentally, two of my most-played CD's) that really showcases all of her different stylistic abilities.
'Evolve'- the best (in my opinion) of her later cd's, especially for showcasing guitar work.
Hope this helped.