"A great, simple, collaborative mindmapping site. Invite other users to share ideas together in real time. It uses html which means that you can use it with most web enabled devices. Sign in using a Google account."
Bamboo DiRT is a tool, service, and collection registry of digital research tools for scholarly use. Developed by Project Bamboo, Bamboo DiRT makes it easy for digital humanists and others conducting digital research to find and compare resources ranging from content management systems to music OCR, statistical analysis packages to mindmapping software.
If you're using mindmapping and brainstorming in the classroom, this list from Mashable is updated and useful. There are a lot of new tools out (many of them paid but some not.) If your students are writing collaboratively, you should have them brainstorming collaboratively before they ever type the first letter of the paper or website.
"Organising information to find clarity is key for making good decisions. This collaborative mind-mapping tool allows multiple users to work together to put together their ideas and resources."
CmapTools is a free program used by colleges around the world for creating concept maps: graphical tools for organizing and representing our knowledge about a particular issue or system. In CmapTools, concepts (boxes or nouns) are linked together by propositions (lines or verbs) to form a network that visually demonstrates connections between issue components. By creating a visual map of what we know, one can open up new ways of understanding how that system functions and how its components interrelate; this is what distinguishes CmapTools from more traditional (e.g., verbal) modes of thinking and communication.
also check http://cmapskm.ihmc.us/servlet/