A small selection of interesting (for varying reasons) books on the blues:
Alyn, G. (1993) 'I Say For Me a Parable' The Oral Autobiography of Mance Lipscomb, Texas Bluesman. New York: Da Capo.
Calt, S. (1994)I'd Rather be the Devil: Skip James and the Blues. New York: Da Capo.
Calt, S. and Wardlow, G.D. (1988)King of the Delta Blues: The Life and Music of Charlie Patton Newton: Rock Chapel Press.
Cook, B. (1995) Listen to the Blues. New York: Da Capo.
Evans, D, (1982) Big Road Blues: Tradition and Creativity in the Folk Blues. New York: Da Capo.
Finn, J. (1986) The Bluesman: The Musical Heritage of Black Men and Women in the Americas. London: Quartet.
Palmer, R. (1981) Deep Blues New York: Viking Press.
Wardlow, G.D. (1998) Chasin' That Devil Music: Searching For the Blues. San Francisco: Miller Freeman Books.
And any number of books by Paul Oliver.