You might want to try the Crowne Plaza.
It is practically on the KuDam, not 5 minutes from KDW on one side, and the zoo on the other, but still manages to remain quite. Excellent service and more than fair prices.
Crown Plaza city centre Berlin
Nürnberger Str 65
Tel.: ++ 49-30-21 007 0
E-Mail: info@cp-berlin.com