As said above:
Half A Wing, Three Engines, and a Prayer by Brian D. O'Neill (expanded version) although the original is great, too - one of my favorites
Fortress in the Sky by Peter M. Bowers - fantastic reference!
Flying Fortress by Edward Jablonski - terrific overall view of the B-17 in combat
Flying Forts by Martin Caidin - not totally historically accurate, but very entertaining. This and Jablonski's book really fueled my interest (obsession?

) with the B-17
The B-17 Flying Fortress Story by Roger A. Freeman with David Osborne - thumbnail sketches of ALL 12,731 Forts built - Essential!
___________________________________________________
Combat Crew memoirs:
A Wing and a Prayer by Harry H. Crosby
Those Who Fall by John Muirhead
Combat Crew by John Comer
Skip Bombing by James T. Murphy with A.B. Feuer - an excellent memoir of the somewhat overlooked use of the B-17 in the Southwest Pacific Theater
and many more ...
___________________________________________________
Miscellaneous/Reference:
Plane Names and Bloody Noses by Ray Bowden - excellent study of the nose art and planes of the 100th Bombardment Group (H)
Or Go Down In Flame - A Navigator's Death Over Schweinfurt by W. Raymond Wood - excellent research some 50 years after the fact
Queens Die Proudly by W.L. White - vintage work on the
very early days of the B-17 in the Pacific
B-17 Flying Fortress Units of the Pacific War by Martin W. Bowman - a good view of the B-17 in the Pacific - this book is incorporated in
Fortress Of The Skies - The B-17 Flying Fortress in Combat which is a good overall reference
B-17 Flying Fortress (Enthusiast Color Series) by Jeff Ethell - lots of cool period color photos
Pride of Seattle - The Story of the First 300 B-17Fs by Steve Birdsall - excellent thumbnail sketches of these B-17s
Claims to Fame - The B-17 Flying Fortress by Steve Birdsall and Roger A. Freeman - excellent reference on the longest-serving B-17s
Any of Roger Freeman or Steve Birdsall's books are excellent.
___________________________________________________
Nose Art:
B-17 Flying Fortress Nose Art Gallery by John M. and Donna Campbell
He!!'s Angels by Steve Birdsall
etc ...
There are a
lot more at Steve Birdsall's B-17 Bookshelf:
http://users.beagle.com.au/stevepb/index.html 