Mark Blake, Comfortably Numb: The Inside Story of Pink Floyd (2008)
This is probably the best book on Pink Floyd. Blake takes a fairly typical approach in this band history/biography, but it's well researched, well written, and comprehensive in following the band from its beginnings through 2007.
Gerald Scarfe, The Making of Pink Floyd: The Wall (2010)
This book's focus is as narrow as the title suggests. And Scarfe is a cartoonist, not a writer. But if you are interested in the album and the film that followed, you'll enjoy this book produced by one of the film's directors.