Apart from Singh's incredibly famous one, I also quite enjoyed _Colossus: The secrets of Bletchley Park_[1] for technical history.
The autobiography of Leo Marks: _Between Silk & Cyanide_[2] was a good (although I suspect quite heavily dramatised & exaggerated) read about the more human elements and flaws of pen & paper crypto used by the allied resistance groups.
The autobiography of Leo Marks: _Between Silk & Cyanide_[2] was a good (although I suspect quite heavily dramatised & exaggerated) read about the more human elements and flaws of pen & paper crypto used by the allied resistance groups.
[1] http://www.amazon.co.uk/Colossus-secrets-Bletchley-code-brea...
[2] http://www.amazon.com/Between-Silk-Cyanide-Codemakers-1941-1...