Potsdamer Platz, once the largest urban development zone in the world, is a great testament to the growth of reunified Germany. it was once the "no man's land" between the Berlin Wall, and now is being redeveloped (nearly complete by now) with high-rise offices, etc.
There is a great museum on-site, called the Info Box. It's a big red building. It talks all about the development of the site, how decisions were made regarding what to put there, how was involved, and the high-tech role. It's very interactive, and take it from me - someone who hates museums - this is worth it.