Matthias Büttner's website features photographs from Germany, Poland, the Czech Republic and China, mainly steam but also endangered species of railcars, diesels and electrics. Well worth a look. The text is in German but it's not difficult to find your way around the site if you don't speak the language.
A German language forum with photos, discussion, news, sightings and much more.
A German language site covering classes 215 - 218 and derivatives, i.e. the bulk of the current DB main line diesel fleet, with technical details, photos, diagrams etc. Registration is required to access some information.
Open access has really taken off in Germany and a myriad of private operators now run trains on the national system. This site helps identify who's who. German Language (Also see Railfaneurope under European Railways for similar info in English).