Thought I'd start a thread where people can recommend books that they have read, preferably at least remotely related to puzzles, ciphers and codes, but not limited to.
So I'll start with the best book I've read about cryptology and ciphers.
Simon Singh - The Code Book
This book, imo, is a very good summary of the history of cryptology, ciphers and codebreaking. It covers just about every significant development in the field from "Shave the man's head, tattoo the message on his head, wait until the hair grows back and send him on his way to be shaved again on the receiving end", to quantum cryptography. Singh writes in a way that is both easy to understand and fun to read, and I will recommend this book to any remotely interested in the topic.