This drives a couple of LEDs (or a bi-colour LED) attached to a spare COM port. You could even connect the LEDs in the PC case to the COM port. This then gives you a front-panel indication of run state. If you've shut the machine down remotely, you can tell when it's OK to power it off.
Even better, you can connect a switch up to the serial port, and shut the machine down from the front panel. Why not use an otherwise useless switch, like reset? :-)
Here's the wiring diagram:
Here's the source, makefile, software installation instructions.
Comments? Problems? Mail me.