The NARA in Washington, D.C. has some declassified records that may be of interest to a few here. The page itself is daunting, lsting a huge number of documents. On the left side of the page is some numbering, of which I'll mention a few of interest.
NR 8 German Air Codes
NR 22 3 Digit Code Book Taken From ME410 Aircraft
NR 98 German Codes For Freya And Wurzburg Signals
NR 292 German Fighter Slang Code
Also see, NR 783, 785, and 798.
Definitely not for the feint of heart, but may be of value if examined in pieces over a number of days. Unfortunately, it is not just about the Luftwaffe.
http://www.nsa.gov/public/publi00004.cfm
Ed