I never heard about Havel until some friends and me checked out the google earth for a trip at the weekend. We went there in the german winter, oh yes...in the winter. I loved this place because is a small city island with a lake (which was frozen at that time) and with lovely houses and an old mill. I have never been there in the summer but i can imagine how wonderful would be.
Kw is a great art institute situated at the backyard of a very eastern part of town, place for many other small galleries. Auguststrasse is worth the walk and Kw is worth the stop.
Rixdorf is definitely my favourite area of Berlin, because it is a historic village within in Berlin. At the moment it is under heavy construction, and I found this strange, nearly taken-down building sitting in the middle of the quaint neighbourhood.