I thinking about buying this power outlet, which is manageable via usb.
http://www.gembird.cn/main.asp?mode=item&N=5915
 
There is this open source project which lets you control it from linux
oder mac os:
http://sispmctl.sourceforge.net/
 
Maybe I can think of some cool ways to use it (turn a light on if new
email arrives or something similar).