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.