Just finished documenting two plotter projects I thought I'd share.
The first one is a Polar Plotter, meaning it has a rotating, extendable arm, that can be programmed to run a plot sequence. It supports drawing lines, rects, circles and text. The font used when drawing text is created with a Java program where you can load any truetype font and generate code that's useful for the Arduino program. The documentation might be useful for someone doing something similar. I think the construction or the font generation might be highlights of interest otherwise. The docs and full code is available on GitHub: http://roxen.github.com/polar-plotter/. There's also a video there.
The other project is a Live Plotter that is controlled from a browser. It has more of a traditional construction than the Polar Plotter. The main feature is that you can draw on an HTML5 canvas in the browser which sends drawing commands via a websocket to a server which in turn sends the commands to the Arduino board via serial comm using the usb cable. This project is documented at http://roxen.github.com/live-plotter/ and does also have a video.