Maybe not as complicated as you are looking for... but, I once bought a bunch of flashing red LEDs cheap ($5/100). They seem to flash ar different frequencies. I've been using 5 wired in parallel to discharge a small rechargable lithium battery I have been playing with for a couple of weeks (using LEDs as solar cells). Get pretty interesting, and apparently random patterns.
There are are dozens of 2 transistor circuits to flash LEDs on the web, will take a look later, might have on on my HD to post. But if you put together 2 identical circuits, they will flash at slightly different frequencies due to component tolerances (caps and resistors).
Have seen, and likely have a copy, of a circuit using a 4xxx CMOS chip, that flashes randomly. Just seemed like a lot of pins for something I could do with an 8-pin AVR chip.