I can't begin to tell you the joy I've had in pursuing the photography section of Half Price Books. I've found many, many good (if not great) older (70s) books on photography, and for basically pennies! Thing is, you pay half of the cover price, and since many of these older books have a price of $12 - $14, well, let's just say you're getting a lot of bang for your buck!

EDIT: I forgot to login before posting this the first time.