As part of the software package provided with the Wacom Intuos 4 tablet I purchased recently, Autodesk Sketchbook Express 2011 is a fantastic product.
A simple interface and the common tools one would expect in a drawing program really help to make this application simple to use for almost any budding digital artist. What I found particularly great was the ability to use this application without ever using any other interface device than the pen and tablet. I've discovered that I never have to reach for the keyboard when I am drawing. Of course, I expected that the makers of AutoCAD would also know a thing or two about drawing in general.
A trial version of the application is available for download and if you have a pen and tablet, you might want to try it out and discover this great tool for yourself.