Cryptonomicon, by neal stephenson
this is probably the best SF book I've ever read. Most science fiction gets bogged down in needless technical jargon or is just too fantastical to be very compelling. Cryptonomicon is set in the real world, involving real people and events, and still is good science fiction. Stephenson gives a crash course in cryptography throughout the book, and doesnt dumb down a single paragraph. the storyline follows about four main characters through various times and places, and slowly ties them together through careful placement. ive not finished it yet (still fifty pages to go) but if its anything like Stephenson's earlier work it will end a bit too quickly but still well resolved.