Last year I read a book I really enjoyed. It was called "The Code Book: The Science of Secrecy from Ancient Egypt to Quantum Cryptography". It was basically the history of cryptography in a nutshell. One of the subject that I found completely fasinating was the use of "Enigma" machines during World War II to encrypt messages. Germany had some brilliant minds creating these devices. Well there are only a view in existance today. So it's something I could get my hands on and play with, that was until I found a Virtual Enigma Machine. So now I can play with one to my geeks/hearts content.

Update: There is quite an interesting discussing on the Enigma at digg.com if you'd like to read more about it.