Brainstorming Tools
This is the easiest, free brainstorming/ graphic organizer tool I've found on the Internet. Highly recommended.
Easy customization, but it is a paid program. Also has Kidspiration, which is the Elementary version of graphic organizers, and Webspiration which is exclusively online.
Here's another online graphic organizer, but this website provides the research supporting why graphic organizers work. It's an all-inclusive site: the tool, how to use it, and why it works.