Hi Garbitsch,
first of all, of course you are right Brandenburg Gate and Reichstag are a must.
Check Point Charlie in my opinion is not much to see nower days, apart from the Museum about the Berlin Wall.
A nice place is the remainders of the Berlin Wall called the "East Side Gallery" (original name, not translated
) to be found near the main train station.
Holocaust Museum, well what do you mean, there is the brand new monument, which I havent seen yet, or the Jewish Museum?
The latter is well worth a visit. Theres lots of other museums as well: the New National gallery, designed by Mies van der Rohe (in the western part) and the Old National Gallery (in the eastern part) and the most famous Pergamon Museum which actually is a must as well.
If you are more into buildings etc then I recommend
Charlottenburg Palaca, Bellevue Palace, TV Tower (East) with a great view over the city, 1936 Olympic Stadium, currently reconstructed for World Cup 2006.
Excessive information about all these museums and sights and the city itself, along with useful tips are to be found here in english:
http://www.berlin.de/english/visitors/index.html
Other, not so good pages are these ones, but I guess you already came across them....
http://www.travelocity.co.uk/TEU_destGu ... 1,00.html;
http://www.opodo.co.uk/otpbvpl/Jsp/opodo/StrutsServlet/
travelGuides?BV_SessionID=@@@@2073888188.1116448071@@@@&BV_EngineID=ccdiaddejhhklelcefecenhdhhldfnn.0
If you happen to have a few more days then the city of Potsdam is a nice place to see. More historical background. Also the Villa Wannsee in Berlin.
In case I can be of any more help, just let me know.
Have a nice trip!