Frommer's suggested itinerary:

If You Have 1 Day -- Get up early and visit the Brandenburg Gate, symbol of Berlin, then walk down Unter den Linden and have coffee and pastry at one of the cafes along the edges off this boulevard. Visit the Gemäldegalerie to see some of the world's greatest masterpieces. Afterward, go explore Schloss Charlottenburg, one of the finest examples of baroque architecture in Germany. In the evening, walk along the Kurfürstendamm, visit the Kaiser Wilhelm Memorial Church, and dine in a local restaurant.