I've been working on a method to create an automated system for switching things on and off via the computer as part of a hobby.
I didn't realise how "easy" and interesting it would be. A USB board (Arduino Duemilanove) can be bought for less than Ã,£30 (Link (http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=6961655)) which you can control directly with the computer , program the onboard chip directly, or control via serial though a number of programming languages (I started learning Python this morning).
I realised that it would make a cheap project for any motivated child to for instance make a clapper switch, or build a little robot etc. Learning a little bit of programming and electronics as they go.
It's not just for kids either, you can buy "shields" you plug in which can give it functions like GPS, Ethernet internet access, Ultrasonic distance sensors etc. To make some really sophisticated projects. I'm working on automating a biodiesel processor with mine, but the options are endless. I know it's not to most people's tastes, but who knows.