You wrote 2 hours ago
Mac Users:
I just found a free brainstorming (or 'mind-mapping'

program online. I've used it and fonud it useful. You can set a time limit, say 5 minutes, then type in your topic, and then you have just that amount of time to spew out ideas in a list format.
Mac OS X 10.4 and later.
http://www.conceptdraw.com/labs/index.php/2007/03/ 22/brainstorm-lite-is-released/
FOR PC
I found a free app for PC, called FreeMind. You can read all about it and see screenshots before downloading at:
http://freemind.sourceforge.net/wiki/index.php/Mai n_Page
FOR MAC AND PC
This looks interesting. For Mac and PC, a freeware program called Celtx. Here is the blurb from their website:
"Celtx is the world's first fully integrated solution for media pre-production and collaboration. It replaces old fashioned 'paper, pen & binder' media creation with a digital approach to writing and organizing that's more complete, simpler to work with, and easier to share."
http://www.celtx.com/overview.html
I've been playing with it for a bit this evening and it's cool!