About.com – German traffic signs explained
Brian’s Guide to getting around in Germany – An english site aimed at english speakers; it explains all you need to know about getting around in Germany.
Volu – German traffic regulations explained to the foreigners.
How to Germany – Driving in Germany explained
Dashboard lights – Dashboard lights explained
Driving Test Success – Dashboard Warning lights
All TRavel Germany – Road Signs and Traffic Signals
myFührerschein – Online preparation for the theory exam, including questionnaires; works best on Mozilla and Internet Explorer. The material is in english, german and turkish.
Fahrschule.de – Give a couple of free exam samples, and for €20 Euros offers all the questionnaires and many other exam samples.
Aral Führerschein – Online exam preparation
The apple store also has some very nice apps, check out iFahrschule, it goes for €12,99 and is very helpful