Working for a company that prints a ton of business cards I have had some time to think about different business cards I would like to make. As I am a programmer a very interesting one would be to make a set of cards each that have a different program on it. Granted you could use each pixel to store data, but that isn't very interesting, much cooler would be to limit yourself to what users could read with their eyes. With that constraint you can actually fit somewhere around 6K of text on the card. At this point it is less about toy programs, but more about interesting ones and how you display them artistically. Some different ideas include a C compiler, lisp interpreter, and vm. Granted they might all be limited in one way or another, but it would still be a neat card.
Ray tracing on a business card