Oh Berlin is probably my favorite city in Germany!!! How long are you going to be in the city...I mean hit the basics, Potsdamer Platz, Brandenburg Gate, Reichstag (make sure to go inside and go up into the dome part, awesome view the city), Berliner Dom, Alexanderplatz, Checkpoint Charlie, Gendarnmarkt, Ku'damm, Eastside Gallery....there is also a ton of museums. The city is really easy to walk around and alot of the sights are near each other....also the U-Bahn is pretty easy to use. If you have limited time...do a city bus tour. They tell you so much about the city and you can get off at any point....As for night life, to be honest, I dont really know, all my friends live just outside the city so we never really hit the clubs in the center of the city. The atmosphere in the city is so alive...i just love it!!! How's the German??? hahaha
As for Munich, I live in northern Germany. I have been there a few times. Hofbrauhaus, best Oktoberfest feeling ever!!, Marianplatz, the Olympiapark, and the Allianz Arena where they just played the world cup!!! You should take a day trip to Fuessen and Ludwig's Castle. Really close to Austrian border, could head to Salzburg from there!!! and you are getting into the Alps as well...so the landscape is great!! Oh hope you love it!!! Been backpacking around Europe a few times....best time of life...when are you leaveing???