Cryptonomicon (Neal Stephenson)

This is a big book with an amazing number of threads: math, computers, cryptography, World War II, treasure hunting, data security, hacking, and more. At first, the two halves of the story (WWII and present day) seem connected only by the last names of some of the characters and the general theme of cryptography, but by the end everything has come together. I enjoyed all the science geekery, presented in a way that is accessible but also accurate, and was completely caught up in the personal stories of loyalty, trust, and love. Highly recommended.