If anyone gets anywhere near Berlin, you have to try the Marriott at Pottsdammer Platz. Simply one of the best I have found and the Executive Lounge makes it even better. Once inside the lounge you are really treated like a King and its hard not to feel at home there.
The hotel is right on the site of the old Berlin Wall and right down the street from numerous attractions. A very nice location.
Agreed - the Berlin Marriott is a winner. And, if you want to burn more money, the Ritz Carlton is literally next door. Great location, generally, and particularly if you use the excellent public transportation.
Be sure to visit Museum Island, and spend some time in the Pergamon Museum.
But give the HiFlyer Balloon (not far from Checkpoint Charlie) a try - it's a lot of fun and a great view.