The Lux 11, part of the Design Hotels group, is my favorite hotel in Berlin. I stayed there in December of 2008 for New Years Eve and the location, design, and restaurant were all top notch.
The bar in the restaurant offered amazing inventive cocktails, and food was delicious. They have a store with cool, unique fashion items, and a relaxing spa. I stayed in an executive suite with a great balcony and the premiere suite and penthouses above are really breathtaking with simple, modern design.