Although still in beta testing, popplet is well worth checking out.

By applying for a tester code that will arrive in a day or two, users can take this site for sharing ideas visually for a test drive. This video explains more:

If you don’t want to try the test model, you can stay in touch with popplet news via email, Facebook, Twitter, Vimeo or Tumblr. As popplet lite is also available as a free iPad app, schools and teachers that have access to them might like to investigate further.