One of the best online whiteboarding sites that I have come across. Many great features including an etherpad, equation editor, and multiple backgrounds to write on (webpage, uploaded image, uploaded document,etc)
Collaborate online with Google Docs. Create documents in Powerpoint, Word and Excel and share them with your students. Students can create essays together, construct presentations and post them online with a designated URL. Google also offers collaborative calendars, photo slide shows, personalized maps, scholarly research, customizable home page and many apps.
Great message board application - similar to Lino and Wallwisher. Has added functionality such as post by email, chatting with participants, and polling.