I've been using this site for a while now and it really helps me structure my ideas better. (and it saves a lot of paper!)
bubbl.us is a Flash-driven web app where you can easily make a flowchart. I love that it's keyboard-friendly (Enter to create a child bubble, Tab to create a sibling bubble).
I can export to XML, JPG or PNG or print it.
I can share it so other people can view or modify it.
+ more features
If you wanna see it in action, here are some videos:
http://www.youtube.com/results?search_query=bubbl.us&search=Search
But it will take you less time to master it than it'll take you to load a video. ;)