I've been wanting to improve my digital drawing and painting skills for a long time now and did lots of googling trying to find something affordable. Instead, I found this! It's called www.ctrlpaint.com It's a free video library by Matt Kohr, where you can follow the short videos doing basic homework exercises to train your hand and brain, and the exercises get more and more developed as you go along. You learn all sorts of cool things like traditional drawing, painting, composition and more. I never had formal training as a digital artist, so these are very cool. :D
If you're feeling like you need some improvement, check 'em out.