Witeboard - A real-time whiteboard for your team. No signups required.
Garbage - In my opinion, poor quality Whiteboard paint, do not buy
Whiteboard Fox - Simple Online Whiteboard
Ziteboard - Ziteboard is an zoomable online whiteboard that lets team to collaborate in real-time.
Mural - MURAL is a visual collaboration workspace for modern teams.
Idea Paint - Create a usable, interactive space on any flat surface