Home automation kit
If you want a reasonably simple way to experiment with using the Pi to control your home check out the Tellstick.
The Telldus Tellstick is a USB transmitter that can be used to control electronics and lights around your home.
It works by sending a radio signal to wall-plugs with built-in receivers to switch them on and off.
With some coding it's possible to set items around your home to turn on and off at certain times or power items up and down over the internet.
Code for setting up the Tellstick on the Pi - running Raspbian "Wheezy" 3.1.9+ - can be found here.