A much improved version of this one: http://openprocessing.org/visuals/?visualID=53004
It arranges them with simulated annealing. Each circle moves around a bit - more, if the temperature is high, and less, if the temperature is low. Smaller circles can move faster. The temperature is displayed as a transparent bar on the left.
- click the mouse to reset, and change the way the temperature changes: asymptotic cooling, linear cooling, oscillating, or controlled by the mouse
To tweak this sketch, first download it.
Make your updates, then upload your tweak!