[FrozenCow]

I was looking for the same thing and found this: http://www.falstad.com/circuit/

It shows blocks traveling across wires/circuits. You can create your own circuits and see what happens. It's not just for logic, but you can see how analog circuits operate as well. The speed of the blocks represents the current flowing and the color of the wires represents the voltage.

I wish more stuff like this was available for circuitry. It gives a nice basic intuition how things work and shows why I need to place a resistor in front of a LED.