Books - Fiction

The Emperor's General  by  James Webb

Enigma  by  Robert Harris

Books - Non Fiction

Alan Turing: The Enigma  by  Andrew Hodges

Applied Cryptography  by  Bruce Schneier

Between Silk and Cyanide  by  Leo Marks

The Code Book  by  Simon Singh

The Codebreakers  by  David Kahn

Crypto  by  Steven Levy

The Emperor's Codes  by  Michael Smith

Enigma: The Battle for the Code  by  Hugh Sebag-Montefiore

Station X  by  Michael Smith

Websites

The official Cryptonomicon site

www.cryptonomicon.org

Try the Pontifex cipher yourself
http://www.carumba.org/hacks/pontifex/pontifex.cgi

www.counterpane.com

Bletchley Park
http://www.bletchleypark.org.uk/

http://www.codesandciphers.org.uk/

Alan Turing
www.turing.org.uk/turing/

Two Enigma emulators

http://homepages.tesco.net/~andycarlson/enigma/enigma_j.html

http://www.ugrad.cs.jhu.edu/~russell/classes/enigma/