Don't forget the Zone System. He and his group f/64 really changed the science and art of photography. I was in a Half Price book store in Overland Park, KS a couple of weeks ago and they had The Camera, The Negative and The Print books for about $15 each, and they were in pretty good condition. If I didn't already own them, I would have bought the set.
Interesting! I was in Half-Price Books in Arlington, TX today and saw a set of the three books in mint condition and got the set of all three for $24. Apparently, the previous owner never even thumbed through the pages.