A few more to add to the mix:
I second the motion on the inclusion of Glen Campbell and Ledbelly - awesome 12-string stylists.

Mark Knopfler should be further up the list

Spider John Koerner and Mississippi John Hurt, who define acoustice blues.

Joe Satriani, in a class by himself in realizing the melodic potential of the electric guitar;

And finally, where is Phil Keagy? Saw him in concert about 15 years ago, blew me away with his virtuosity; he had more sounds coming out of that electric guitar than I thought possible. Of course, his religious stance may not have "fit" with whoever judges these things at Rolling Stone...