Not necessarily in any order and I am assuming in the rock genre:
1) David Gilmour - Simply beautiful sonics, check the solo out to Comfortably Numb, the 1994 Pulse tour among his other great works. Probably one of my favorite vocalists too.
2) Jimi Hendrix - First guy to really go outside the box on guitar styles... it's maybe hard today for some younger people to see how different he played, we are used to the sounds he got from his guitar but back when he started it was all new.
3) Pete Townshend - Way underrated... even his power chords have melody re: Quick One While He Is Away and again, another great singer too, just listen to Let My Love Open The Door
4) SRV - Loved his style, RIP, for moving guitar work see his Little Wing Fender tribute and any time he played with his brother.
5) Jimmy Page - The most fluid guitarist... he hardly looks like he is trying and out comes "The Hammer of the Gods" from his Gibson. Watch him in the 79 Knebworth performance of R&R... so fluid!
6) Mark Knopfler - I nearly fell over when I first learned he doesn't use a pick... wow! Multi-string master and very versatile in style. Love when he plays the Red Strat... "girl you looked so pretty to me..."
7) Kevin Cadogan - "Who?" Yeah I really like this guy, for those who don't know he was with 3EB in their heyday. He is the master at alternate tuned guitars and the resulting complementary sonics that go with his tuning. Master works include God of Wine and Background.
8) Steve Jones - "Are you serious?" Dead serious... he delivers power chords that include the low E string like a mailed fist. Even if you hate punk... his guitar work on The Bollocks is legendary. The rumor it was all Chris Spedding is not true, Jones could play.
9) Mick Ronson - RIP... Bowie always surrounds himself with some of the best guitarists in the business (Fripp, Gabrels, etc.)... Ronson was no exception... jittery and edgy, very curious sonics like they were from outer space which, of course, worked well for the Spiders phase. Watch him cover Fripp's guitar work on Heroes at the Freddy Mercury tribute like it was his own. Let's Spend the Night Together (RS cover) again with the edgy dive bomb sonics... and Ziggy too.
10) Neil Young - Melodic power chords and equally melodic solo work, again one of the guys that is so fluid, like the guitar is a part of his body... master guitar works include: Hurricane, Hey Hey, etc.
Guitarists that could easily go up top, I just flashed the list out quickly: May, Richards, Buckingham, a lot of the metal guys out there (Wylde, Rhoades [RIP], etc.), special mention who I should have put up top is **** Dale, he is a favorite too big time. I could go on... like we all could I am sure.