Der Deutsch-Kurzhaar by Georgina Byrne is back in print for the first time in years!!! This is one of the greatest GSP books ever written, and is a must have for any serious breeder or avid breed fan (I am the latter). I have tried to find a used copy for a while, but they are either impossible to find, or several hundred dollars!
Here is the site where you can purchase a re-print of her comprehensive masterpiece. She covers the breed history, genetics, conformation, training, hunting, just about everything you could want in a huge, beautifully illustrated book. I highly recommend!