Tai Shimizu has Inkist (iTunes Link) for the iPad in the iTunes App Store for FREE (regularly $1.99) for a limited time.

nkist lets you paint on your iPad with highly customizable brushes and tools you expect from advanced painting software. Inkist eschews the trend of hiding interface elements from you, and presents you with everything you need up front. This minimizes the number of taps needed to switch between tools and provides you with a faster, more streamlined drawing experience.