I know many people have suggested them, but I'd like to put a little more detail into how it might work effectively to allow for central power supplying.
Monitors total EU that has gone through the line. Configurable to give redstone output when a limit has been reached. Able to be reset through an input from an adjacent toll kiosk, or by the person who placed it.
If placed near the EU-Monitor, this machine allows for payment to allow sending EU from a central power source. This can also be used to provide a redstone output alternatively for use as a toll booth for certain facilities such as a mob farm or a subway system on larger servers.