For you artists out there, I've run across a couple of really nifty programs. Actually, I ran across them a while ago, and have been using them for some time now. But I'm just now getting around to writing about them.
The first one is called MyPaint. It's a small paint program written in Python and C. In some respects it is quite primitive (it doesn't support layers, for instance), but in other ways it's extraordinarily advanced (its brush system is insane). However, the thing I like best about it is that it has an infinite canvas, meaning that if you run out of room you can simply scroll over and keep painting.
I use MyPaint as a digital sketchbook. You can assign any brush/color combo to the number keys on the keyboard, so I simply assign a black pencil brush to 1 and a white paint brush (eraser) to 2, and then sketch away. I like to close all the windows except the drawing area and then maximize it so that I have the maximum drawing area. Then I can just sketch to my hearts content without ever running out of room thanks to the infinite canvas.
I don't recommend mypaint as a full-fledged paint program, but as a simple sketch program I have found nothing that beats it. Seriously. I mean it. This is the ultimate sketch program. Ever. The only thing that could make it better would be if it recognized the back end of my stylus as an eraser (unfortunately it treats it the same as the tip).
The second program is called Pencil. Pencil is a 2D animation program, and is quite intuitive. I use it now both for playing with 2d animation on its own, as well as to help me plan out my 3d animated peices. It's a little glitchy here-and-there, but I haven't run into any major problems. And the simple and intuitive approach of the program makes it a joy to work with.