Minecraft: Bat Powered Random Number Generator
Since Minecraft 1.4 Bats on minecart can move freely, here is my original Bat Powered Random Number Generator (on YouTube)! The design can be compacted. Uses minecart, not Bats on pressure plate (fails on MC 1.4.2)
Pros:
It is a True Random Number Generator in Minecraft universe.
Very easy to build on Creative (No logic circuits!)
Cons:
Getting too far out will cause Bats to despawn, stopping the RNG.
Getting Bats into minecart is very difficult on Survival.
Noisy minecart and annoying Bats sounds.