The tools on this page are designed to help develop student thinking skills. It is quite an ecclectic mix so make sure you look at the potential of each tool.
1.
Thinkature - It is difficult to categorize this tool as it includes several different elements. The basic idea is that students use an online whiteboard to show their thinking. You begin by posting cards onto the whiteboard. These cards can be text or image and can be colour coded. You can then draw connecting lines between the different cards. There is also a chat function on the page, either text or voice, which again will facilitate collaboration. Collaborators can be invited by e-mail. I have not tried to share the URL but this may possible be another way to share the whiteboard. I would be interested to hear how you think you could use this tool.
Click Here to see an example workspace.
2.
Bubble.us -
This presents itself as a Brainstorming tool but as you can see from the example below it is presented in Mindmap form. Fairly easy to use although there are no images or graphics allowed. I would suggest this may be a good tool for an interactive whiteboard for an introduction or plenary session where you don't have the time to introduce graphics.