We've discussed how to automate your home with X10 before, but if you're unhappy with its limitations and are willing to roll up your sleeves, you can tweak nearly any electrical device to communicate with your computer.
Over at DIY web site Instructables, user indestructable thoroughly describes the process of connecting an electrical device to your computer and controlling it with some simple programming. The set-up relies on a USB relay device such as USBmicro's U451, and you'll need some wire, wire cutters, crimpers and nuts to hook it all up.
His set up is fairly simple, but he does a good job of explaining the mechanics behind the USB relay device and the programming software he uses (which, by the way, is free). The resulting programs aren't necessarily pretty, but if you're willing to learn, you can get pretty complex. And, most importantly, you can do it with almost anything that plugs into the wall. Hit the link for the full how-to, and let us know your favourite home automation tips in the comments.
Computer Control of AC Devices [Instructables]