I usually check metaltix.de or eventim.de if I look for tours. The tour calendar of the Rock Hard Magazine is good too.
http://www.rockhard.de/live/abfahrplan.html - just type in Berlin and when you get the list, scroll down and click on the bottom link to get more dates. Or you go check out the band websites of course.
August is usually the driest months regarding concerts. Good luck!