I've been obsessed with Langton's ant for a good solid decade now. My latest creation is a few years old now, but occasionally I go back and add new commands. It's inspired by Langton's ant, but it operates in 45 degree increments, has the ability to fork, conditionally execute instructions, has colors, and a bunch of other interesting things. You can see it in action at http://demoseen.com/langton/#.FP$!!!!!!!!!!!!!!!!!!!!~ and there's a simple instruction listing at the bottom of the page.

It's quite a departure from the original, but you can make absolutely gorgeous images with some simple instructions.