While I have used DimDim, Elluminate, and Skype, I signed up for DabbleBoard today after hearing how the students in Monika Hardy’s classroom were using the tool to collaborate on math problems.  DabbleBoard is a free online whiteboard that loads quickly and is easy to use.  It is possible to share audio and video through Tokbox which is linked to the DabbleBoard page.  Multiple students may login simultaneously and share their ideas.  I have embedded the link on our class blog so that students will have easy access to our homepage.