Online Etch-a-Sketch

This is better than the real thing because you can use arrow keys instead of knobs to draw with. No more dropping it on the floor, either.

Best of all, with computer sketching, you can get screenshots to preserve your work. Firefox users, for example, can use an extension called Page Saver for easy screenshots. Unlike most screen capturing software, it can be set to capture the entire page even on very long pages. (Use PNG format for best results.)