That's really cool -- I love 'lattice' type patterns. This is my current favorite, because it seems to terminate (stabilize) and then does one last little bit. Runs for a good while before it 'terminates', as well. http://demoseen.com/langton/#.$!~PF!!!!.
That's really, really cool. I want to make a gallery system for these, where people can submit theirs and others can modify from there. Btw, I just added a polar mode (the grid is treated as polar coordinates, and converted from there); the & instruction switches to polar and _ brings it back to cartesian, so you can actually blend the two. http://demoseen.com/langton/#&m.$!~PFP!!..
This is the best pattern I've been able to come up with so far:
http://demoseen.com/langton/#..rr@<>@!!@@