Before yesterday I had no idea what a K8055 was, but it turns out it is exactly what I've always wanted, and after pressing buttons and lighting up various LEDs for the past half-hour I am convinced everyone should have one!
Basically the K8055 provides a method of sending and receiving digital and analogue inputs and outputs from a computer.
The pleasure of the K8055 is that it is so easy to use (especially in comparison with the previously discussed USB thermometer that I'm Twittering). Not only does it come with the required drivers and a demo program, but the source code for the demo program is provided in a number of languages.
Now I need to decide on what I want to input or output.
Currently I'm thinking either a bulb that brightens and dims according to the mood of Wolverhampton (using a sentiment analysis of Twitter), or maybe just a big "ARGGHHH!!!" button that I can hit every time I get annoyed. But with a host of switches and sensors available (e.g., infrared & motion detectors) the possibilities are seemingly endless, so any other suggests are welcome.