This is a really good thread. I am torn between 4 or 5 books, and given how much they each cost - I certainly cant buy all of them!
Brewing: Science and Practice
Essays in Brewing Science
Michael Lewis's Brewing, 2nd Edition
Handbook of Brewing, Second Edition (really cant justify this one atm)
The Brewers' Handbook: The Complete Book to Brewing Beer (looks good but not as BIG as those above...