Recently I took part in a brainstorming session about the design of a c# application. We chose to use Class Responsibility Collaboration (CRC) Cards to come up with our basic object model and get the responsibilities straight. I have used this technique a few times before, and always with good results.

I think CRC Cards help to keep the brainstorming focused and at the end of the session you have your model ready, on paper. You should definately give this technique a try when you have to do some (re)designing or refactoring.