I found an old GSP file with a bunch geometric fractals in them - I thought that some of them looked nice, so I've posted them here. If you'd like to try them out, you can get the GSP file
here - for the most part, they involve pretty standard use of the "iterate" feature.
Animating them in random ways creates some strange looking forms - the same sketch that produces the pentagon fractal above also gives the one below.
The same sketch that gives the snowflake-like pattern at the top of the post gives this odd looking sponge: