Been to Berlin a couple of times. Brilliant City.
Check out the usual suspects of the Reichstag, Brandenburg Gate, Check Point Charlie.
I would also recommend the Halocaust Memorial, very powerful place. Also the Sony Centre, Berlin Zoo and the television tower in the old Eastern side of the city. You can go to the top and get some great city views and there's a bar!!!!! behind the tv tower is alexander platz, which is where they shot some of the scenes from the Bourne Supremacy.
Outside the zoo is an old bombed out church, which is quite a popular photographic subject. KaDeWee is up the road also which is the largest department store in europe.
There are various places where you can still see part of the old Berlin Wall, around the check point charlie area.
The main station is a pretty spectacular building, think is it the biggest in europe and some of the embassy buildings, especially the nordic group are pretty cool.
The Underground or U-Bahn is great, although you stamp your ticket before you get on the trains, not after you get off!!!!
We took a bus tour which was also very imformative and you can get on and off when you want.
'Felix' is a pretty happening place for the night time, which is near brandenburg
Enjoy