From my personal experience I can recommend a couple of hotels in Dusseldorf.

The first would be the Mercure Dusseldorf City Center which is right across the street from the main train station in Dusseldorf. The rooms aren't the largest, but it is very stylish and comfortable and right in the heart of the city.
http://www.mercure.com/gb/hotel-5373...er/index.shtml

The second would be the Novotel Dusseldorf City West. While this is not near the train station, there is a metro stop right across from the hotel and it is a short (15 minute) ride to the train station from there. The metro drops you off directly underneath the train station. I enjoyed this hotel very much. The restaurant is very nice and just a great hotel. It exceeded my expectations.
http://www.novotel.com/gb/hotel-3279...rn/index.shtml

If you have any questions on either hotel please let me know.