Berlin's Business Aviation field, as somebody was asking above, is Schönhagen if you don't want to go straight to Schönefeld.
Frankfurt's is Egelsbach, or Mainz-Finthen or Söllingen, depends where you go to.
Munich's is Oberpfaffenhofen or Augsburg. Or Manching.
There is a lot of choices. Plenty of more really small airfields all around the country. Plus mil airfields that sometimes can be used by special permission too if you convince their commanding officers.