The RaspberryPi has a lot going for it but you can get started with a small ARM computer without the hassle of ordering from one or two venders and waiting for a bare board computer that also needs a power supply, case, memory storage, USB cable, HDMI cable, ethernet cable, etc. One alternative is a Pogo Plug. In the USA, you can order one for $20-40 from a number of sellers. It comes with a case, multiple USB ports, and a built-in power supply. You will need an ethernet cable but otherwise you’re all set. The one thing you can’t do with it easily compared to a RaspberryPi is hook it up to a display. But if you wanted a small Linux-based computer that sips electricity and is ready to go hardware-wise out of the box it fits the bill.
The software on the Pogo Plug can be easily changed to an ARM build of Arch Linux with specific instructions at archlinuxarm.org. After the install, I was able to hook up an external drive and setup bittorrent and other applications that are nice to have running all the time but don’t need a lot of computing resources. It is a shame leaving a full desktop powered on using 60-100 watts but a small ARM device like this uses something close to 10-15 watts.