Remote Power On/Off Switch
Take a look at the X10 devices. Its an older protocol that uses your power lines to transmit signals to each X10 adapter (a small plug with a couple of dials to set an id code). So if you use a X10 plug to connect your PC's AC, then you can toggle the power to that switch remotely. Options for remote are over the phone, ethernet (via Firecracker PC serial adapter) and wireless remote pad.