Board800 is a free, web based interactive white board that can be used by multiple users at the same time.
It is very easy to use and you can save your session. Tools include shapes, free drawing, and text. Your session can be saved as an image for later retrieval, archiving, or to embed in a document or web site.
This would be great for distance meetings, distance learning, tutoring, homework help, and much more.
You can also purchase a server version to host yourself for a fee.