Check out this list of some of the best free collaborative Whiteboard iPad apps .
This app provides a sort of shared whiteboard. Just turn on the synchronization and send a link to the document to others and they will be able to see it and add to it using SyncSpace. The resulting finsihed work can be shared on Twitter, Facebook or be emailed as PDF.
This app lets you share ideas, documents and presentations and direct the experience of an audience easily on iPad.