I'm never completely sure that I should post this sort of thing here but I thought it might interest a few people.
If you have a NintendoDS there is a great painting program called Colors.
I have tried it and it works beautifully. It even plays back your drawings.
All the tools are accessed on an overlayed screen which is really efficient.
Drawing directly on the screen makes me pine for a Cintiq to go with ArtRage!!