Here's a great site that includes the video below which is a fascinating look at the use of online communities within the school community!
I really enjoyed the video above and the great information at http://www.teachers.tv.
As a note, Voki, which is mentioned in the video and is a free tool that allows you to create an avatar and have your avatar speak your words is developing an educational version with no ads! If you go to www.voki.com, you can sign up for updates on this new version! By signing up, you may also be among the first to have access to this new educational tool!