Favorite ex-library book: "The Unix Environment" by A. N. Walker. Ex library: AT&T Bell Laboratories, Murray Hill, NY. Cost from Alibris: $1.

Never heard of Alibris, any other good used book sites? I have bought a book from Abebooks: "Object-Oriented Programming: An Evolutionary Approach", by Objective-C creator Brad Cox.

There is a charity bookshop in my city that exclusively sells ex-library books from the city's libraries. It's very tempting to buy the books there due to them usually being in very good condition.