The LEDs, with the built in flash circuit, as mentioned above, each flash at a slightly different rate. I did a 5 x 5 matrix of them, that run of solar yard light circuit. Looks fairly random... The great part is, they are very cheap, in bulk, surplus, and just wire them in parallel. They aren't overly picky about voltage, need about 3 volts for decent brightness, run fine off 6 volts, don't know the max limit though, before they burn. No resistors required to limit current.
**broken link removed**
10 cents each, isn't bad, but you can find bulk deals for half that...