I used to use mind mapping techniques quite a bit. Like most people, I started by simply doodling mind maps on paper to try to organize ideas. Then, I tried MindJet's Mind Manager at a former job. $200 seemed kind of pricey for software to doodle with once I left that former job though. Then, I found the multiplatform (Linux, Mac OS X, Microsoft Windows) Open Source app...

FreeMind - free mind mapping software

...and was able to satify my idea doodling needs. I don't mind-doodle anymore. But, now that I've reminded myself of FreeMind's existence, maybe I should.