Controlling the power from my Mac?

I was wondering if there is any device out there that would let me control the power (110 V) from my iBook via USB. What I want to do is turn on and off the lights or maybe a stereo. Is this possible to do--especially cheaply? I don't want an entire home automation system, just a simple connection. I've considered building a circuit myself and writing the interface in C++ but USB is not easy to code for.