Alchemy is a free drawing program that works wonders for the starting sketch phase of a drawing/painting. You can find it here. It's a small download and oh so worth it. I had a blast using it (spent about 4-5 hours just doodling on it today). I am sure I will be using this a lot more for upcoming paintings.
Here is a side-by-side of the original sketch done in Alchemy and the finished product done in PS.
Elias Jimenez recently issued a challenge to me to draw a character I've been developing each day and post it to our respective blogs. He would do the same with a character he created. It can be a sketch or a full-fledged painting. The art just has to center around that one character. Here's a start of many false starts.