I agree with Pea... for my money, Stevie Ray Vaughn was the greatest guitar player to ever grace this earth. Isn't it a shame that so many great guitarists Died young, and in the prime of their carreers? (Hendrix, Allman, SRV, more that I'm forgetting)
A lot of good names have been put out there, but here of some of my faves that HAVEN"T YET BEEN MENTIONED. This is based mainly on technical ability for their time as well as having that "unmistakeable style" quality discussed earlier, rather than just on being the guitarist for a great band.
Dick Dale, Eddie Van Halen, Warren Haynes (Allman Bros. band / Govt Mule), Mark Knopfler (Dire Straits), Thurston Moore (sonic youth), Dave Davies (the kinks), Eric Johnson, Buddy Guy, John Fogerty (Credence), and no list would be complete without David Gilmour of Pink Floyd.
I like that thing that Joey Santiago does a lot where he plays two pitches a major 2nd apart on two different strings then bends the lower pitch up to meet the higher pitch. I use 'dat shit all the time. Am I doin' it right, sagesquatch?