My attempt at a Sierpinski Triangle. The principle is extremely easy. We start at a corner of the triangle, choose a random corner, and go half way there. Set the pixel there, choose another corner at random, go half way there, etc. After a short while you end up with this hideous fractal.
For added value, color the pixel differently depending on which corner you moved towards right before setting the pixel.
Tested in Opera 10 Beta 1 and FF 3.0.11