Google Earth (Desktop app) has some historical aerial imagery for Berlin, a lot of other German Cities/Warsaw/Gdansk/ from '44,'45,'53

For more coverage look for gray spots in this overview map http://imgur.com/bfvJpR3

Helps a lot to get an idea of the extent of destruction.

Warsaw has coverage for 1935 and 1945.

For Berlin it's helpful to also go to the 1953 imagery to see which structures where demolished.

http://www.google.com/earth/explore/showcase/historical.html