Here’s an interesting site, the Turing Archive for the History of Computing:
The documents that form the historical record of the development of computing are scattered throughout various archives, libraries and museums around the world. Until now, to study these documents required a knowledge of where to look, and a fistful of air tickets. This Virtual Archive contains digital facsimiles of the documents. The Archive places the history of computing, as told by the original documents, onto your own computer screen.
This site also contains a section on codebreaking and a series of reference articles concerning Turing and his work.