Since this thread seems to be open to just awesome guitar players and not who you think is best, Ill put in somebody I don't think has been mentioned.
Christopher Arp, especially because of his great use of odd time signatures and dissonance / odd keys and key changes. They wouldn't let him in Limp Biskit or however you spell that abonimation of a band because he was too good
[You must be logged in to view images. Log in or Register.]
Look up "Imogen's Puzzle pt.2" (homage to
this hilarious old game, I think) if you want to listen to something that doesn't do damage to the eardrums, but "Death, I" has a great intro some sweet transitions.
I also like Zappa as a guitarist and composer. Lots of other ones I think of are already mentioned.