In many ways, buying a raspberry pi is a problem looking for a solution. I knew that I wanted one even when they first came out, but I just needed to find a use for it. An excuse to buy one. I think that all readers will already know what a Raspberry Pi is, but in case you don't, it's a tiny, single-board computer. See wikipedia or raspberrypi.org for more information if you haven't seen one already.
As you can see in this picture, it looks like a basic circuit board, with a few sockets on the top, but it's actually a real computer. It is only about the size of a credit card (actually a little bit bigger and obviously much thicker due to the sockets) but it can run a real linux system, and use a real monitor, keyboard and mouse. It's got an ARM processor, which is more like the processor in a mobile phone than the one in your computer, but still, it's capable of running many things that a netbook can. And it's really cheap, around 35 Euros for the basic board.
You can see a picture of my new Raspberry Pi, with the most important features labelled, on the basics page.
When buying the laptop, the barebone and the netbook, I started out by looking at what I wanted to use the thing for, and used that to decide what to buy. With the Raspberry Pi, I'm going in the opposite direction, trying to find a use for something that I wanted to buy. So I spent quite a bit of time doing research and reading what people were already doing with theirs, and figuring out what I could do with one.
Here are some early ideas for what to try out with this new toy: