Android: Your best thoughts can come to you when you're nowhere near your workspace. If you're carrying an Android phone, Thinking Space is an elegant and convenient way to map out where your mind goes on the go.
Thinking Space does most of what you'd want a desktop mind mapping package to do, and a little more in some cases. You'll figure out the methods for adding and branching thoughts pretty quickly, and if you're already using Freemind, it can read those files, too. Your mind maps are stored on your phone's SD card, but can also be converted to images and sent by email, or uploaded to a cloud-based space Thinking Space has set up.
I've only just started tinkering with Thinking Space, but the How-To Geek has repeatedly advised me that it's a worthy tool for organising thoughts.
Thinking Space is a free download for Android phones, available in the Market and as a QR code scan at its home site.