I have only stayed at the Hilton Berlin, which may not be modest enough for your needs. You may want to check it out anyways, though, because they sometimes have some very reasonable rates. It is a very nice hotel and is in an excellent location.

For must-sees and -dos, just about anywhere in East Berlin is interesting. My most enjoyable experiences were the Pergamon Museum and going up onto the roof and into the dome of the Reichstag. Other recommendations: walking through the Brandenburg Gate and strolling down Unter den Linden, Potsdamer Platz, the chocolate store ( ) across the street from the Hilton, KaDeWe (especially the food section), the Museum at Checkpoint Charlie.

It's a fascinating city - enjoy your visit!