Here's a link to a site that's all about German beer,style descriptions,history,etc;http://www.germanbeerinstitute.com/index.html Real good starting point. It talks about German hops growing as well.
There's the classic styles series by Brewer's Publications: Bavarian Helles, Altbier, Bock, Continental Pilsner, German Wheat Beer, Kolsch, "Oktoberfest, Vienna, Marzen". These however are showing their age a bit. For an overly detailed view on lager beer production there's New Brewing Lager Beer which gets a tad too technical for most people. It covers decoctions and various lagering techniques but has been superseded by more recent research in some ways.