More to explore:
Inkflow - An iPad App for Visual Thinkers
Inkflow on the iPad: Use your finger as a pen to brainstorm and organize ideas.
The free version allows for simple notetaking, black ink, up to 20 pages in an unlimited number of workbooks. For $4.99 you get Plus, including loads of tools, many colors, and unlimited notebook size.
Inkflow: The Visual Thinking App for iPad, iPhone, and iPod Touch - via http://bit.ly/epinner