Tom Graves, Crossroads: The Life and Afterlife of Blues Legend Robert Johnson (2008)
This biography's complete with an introduction by controversial Johnson expert Steve LaVere.
Peter Guralnick, Searching for Robert Johnson (1998)
This is a short primer on the life and legend of Robert Johnson that does more to stoke the flames of the mystery than to dispel the myth. It's a fun read, especially for fans.
Patricia Schroeder, Robert Johnson, Mythmaking and Contemporary American Culture (2004)
This book delves into the elements of Robert Johnson's life that have the least to do with, well, Robert Johnson's actual life. Schroeder argues that the Devil legend has become more and more significant in recent years, and then asks why.
Elijah Wald, Escaping the Delta: Robert Johnson and the Invention of the Blues (2004)
The author deals not only with Johnson's obscure biography, but with the fascinating development of the myth surrounding Johnson and the mainstream perception of the entire history of the blues.