I have used FreeMind for years to gets some of the clutter in my mind into a bit more structured form on paper for consumption of others.
While I have always loved doing this on the desktop and it is actually the easiest way to work, what I have missed is some mobile access to tweak or view mind maps. However I have come across two iOS apps to help in this regard.
This app is a very basic FreeMind viewer. FreeMind files are uploaded to the iphone view a web interface from your desktop.
This is a text heirachical view of the mind map that allows you to add and edit nodes. It can transfer files via Dropbox or the iTunes File Manager. Not visual but you can fiddle a brain storm on the train going home.Now neither of these mobile solutions offer an easy or synchronous experience but both are useful for quick views and small tweaks.