These are the 22 best custom Photoshop brushes I have created in the past two years. This ULTIMATE set includes brushes for pencils, charcoal, oil painting, inking, and watercolor painting. There are three fun bonus brushes as well. You must have some kind of drawing tablet to get full functionality, and the minimum required software for these brushes is Photoshop CS5. I use these every day - you should, too!
I also dug the gumroad store interface. Very little friction. $5.