Compendium is the first free mindmapping program that I've stuck with for more than 3 weeks. I am using it more and more. The only downside is that printing can be awkward. I have solved that issue at work by exporting jpegs to Photoshop. Not everyone will have that ability.
Just for kicks, I created a GTD map here. Once you register, you can publish your maps to the developer's website. It takes very little time to start using. Nonetheless, it is quite a sophisticated piece of work.