Reaction-Diffusion by the Gray-Scott Model (mrob.com)

Also check out http://pmneila.github.io/jsexp/grayscott/, which is linked to at the bottom of this article: https://news.ycombinator.com/item?id=10216124

I had fun last year playing with WebGL implementations of these systems, e.g.

http://bl.ocks.org/robinhouston/ed597847175cf692ecce

http://bl.ocks.org/robinhouston/f2592c6b2e779b26f60d

http://bl.ocks.org/robinhouston/9868d9c8d06cad448bf0

http://bl.ocks.org/robinhouston/e4d6b3b501e4a2811f9f