At my last job, we used to do a lot of Mind Maps to compliment the discussions we had around future product directions, processes, and happy hours ;-) For that we used an AWESOME program from MindJet called "Mind Manager". This is a super-easy program to use, integrates exceptionally well with Office, Windows and Vista Search, and was able to help us better organize our thoughts. I was thinking about buying a copy for my new job as I've got a million projects going at the same time, when I ran into Thoughtex.net. These guys are building a WPF version of a mind mapping tool that is also extremely cool. I haven't completely gotten the hang of the UI, but there seems to be a number of really interesting features:
It's not as fully-featured as Mind Manager, and doesn't integrate with Office, Search and Windows like Mind Manager does, but if you're on a budget, or want to test-drive Mind Mapping for yourself, this program is a great example of a very useful WPF-based application that utilizes a lot of what the .NET platform has to offer. Check it out at http://www.thoughtex.net.