I also love good tools that are free and will promote them to my heart's content. This one is a simple mind mapping tool with a cool add-on. Check it out: www.mindmeister.com gives you the basics..a web-based mind map that has uncomplicated ways to add branches and nodes.
Two bonuses? Good exporting features. One of my fav's is the outline export, so I can take my scattered thoughts-->outline-->research paper. The other fav is the easy mobile phone update. I use it on the iPhone, but it's not an app. It's a called a geistesblitz (www.mindmeister.com/services/tools) and allows you to add an idea to a quick link on the phone and it instantly is placed on your mind map. No more trying to hold the thoughts and place them later.
Here's a copy of a mind map in action...planning for a research project that had lots of arms and legs that I needed to organize.
And the tool to get ideas from the phone to the web-based map:
