I recommend starting with Robert Johnson. He’s the guy that more or less represents the foundation of what we call the blues today. He wasn’t the first or the only, but if you were to trace the roots of blues guitar, it would be difficult to go back much further. Most public libraries will have or can get his recordings. Have fun. :)

There are so many greats that it's difficult to choose just a few names. However, since the ladies are not yet mentioned:

Memphis Minnie (master old blues guitarist, even older than Robert Johnson), Bonnie Raitt,
Susan Tedeschi, Jessie Mae Hemphill, Deborah Coleman, Rory Block, Clara Ghimel, Erja Lytinnen, Beverly 'Guitar' Watkins, Sue Foley, Debbie Davis...

'Blues Guitar Women' is imo a good double-cd sampler. 'Putumayo Presents: Blues Around The World' and 'Mali to Memphis: An African-American Odyssey' are also interesting compilations containing, mainly, hardly known 'blues' artists.

P.S. Concerning lists, if I remember correctly there's one called sth. like 'the hundred greatest blues guitarists'.

I've always loved Stevie Ray Vaughan, Elmore James, Albert Collins, Otis Rush, Eric Clapton, Robert Johnson, Peter Green, Mike Bloomfield, Son House, Buddy Guy.

Being a Texan, I am always a fan of T-Bone Walker, Freddie King, Stevie Ray and Jimmie Vaughn, & Albert Collins. My other favorites include Muddy Waters, John Lee Hooker, BB King, Eric Clapton, Buddy Guy, Jimi Hendrix. Although not legend yet, I am currently into Derek Trucks and Susan Tedeschi - may their children be musical!

Muddy Waters, hands down. But later on he didn't play much in his band, and Jimmy Rogers played a mean slide. BB King still has it. Albert King and Freddie King are great Chicago legends (I prefer Albert). For true legends you need to go back farther to those who influenced the names above: Sonny Boy Williamson, Elmore James, Charley Patton, Son House, Robert Johnson. Check out Corey Harris' first two CDs for contemporary interpretations of country blues by an exceptionally skilled guitar player (who is not doing reggae).

Other old time favorites of mine: Mississippi John Hurt, Leadbelly, Lightnin' Hopkins, Blind Lemon Jefferson, Blind Willie McTell

For current names, I was blown away by two white boys: Derek Trucks (his wife, Susan Tadeschi has a good voice but she can't keep up with Derek when they play together) and Tommy Castro. Kenny Wayne Shepperd is OK but still has a lot to learn.

As with all blues guitar players, to appreciate them you have hear them live. You can't fit their styles and skill into a 3:40 cut on a disc. It's gotta be heard as 10:40 jams and solos.

Robert Nighthawk is DA' BOMB!