This is my new design for a simple device (5x5x7) that utilizes random logic from the game's code, for use in redstone wiring. The device has 8 outputs that can be wired in many different ways, according to the need of the player.

It's possible to make the outputs have even or uneven probabilities from each other. In this example I wire it to have 4 outputs, each with an equal 25% probability.

The device works like this: When the cactus grows, the new cactus growth block is in an invalid spot because there is a sign adjacent to it. This causes the cactus block to break and be thrown in a random direction, and a random velocity (with a set min & max), from the center of the cactus block. The cactus block then lands on one of the 8 outputs, and eventually disappears after a few (?) minutes.

It's important to note that the growth time of the cactus is random. This means at certain times none of the outputs may be triggered or 2 of the outputs will be triggered. Also, I'm quite certain that the 4 corner outputs have a slightly lower probability of being pressed than the 4 side outputs.

This device can be modified in many different ways to suit your needs, including letting the cactus grow taller so that 2 blocks are dropped at once or having several cacti growing in the center.