Saw this on David Lights blog...
Available for 2.99 on the App Store. Is this possibly the cheapest of Autodesk's software?
Autodesk SketchBook Mobile
The Autodesk® SketchBook® Mobile painting and drawing application extends your digital sketchpad to your Apple® iPhone® or Apple iPod touch®. With the same paint engine as Autodesk® SketchBook® Pro software, SketchBook Mobile offers professional-grade painting and drawing tools in a streamlined and intuitive user interface. Use it to digitally capture your ideas as napkin sketches or produce artwork on-the-go.
Website:
http://usa.autodesk.com/adsk/servlet/item?siteID=123112&id=13872203
Video
http://www.youtube.com/watch?v=YwYm5YhA0pQ