Here is a tool worth checking out. Murally allows you to create an image-rich mindmap and invite other users to contribute. Murally logs each user’s contributions, and even allows space for a little chat window.
This could have some interesting uses in the classroom, but also has potential for teachers to collaborate with each other. Murally is a free resource, and given it is relatively new, could become a powerful addition to your Web2 Toolkit in the future.