German ENIGMA Cipher Machine - History of Solving - In Polish and English.

Garat's Hay - Royal British Legion Branch for the Y Wireless Intercept Services.

Bletchley Park - Museum at the site of the World War II codebreaking center, including a project to rebuild Colossus, the all valve computer used to break the ciphers of German High Command.

The TwinTrees Enigma Machine - Enigma emulator for RISC OS

Andy's Enigmatic Web Page - Download an Enigma emulator for Windows

A Cryptographic Compendium - A good breadth description of a lot of cryptography