Looking for a small computer to play around with? Try the Marvell Sheevaplug, a low-powered box that plugs directly to a wall outlet with enough processing power to run some Linux flavor, along with a nifty app or two.
Measuring no larger than the typical power adapter for handheld gadgets, it fits a functional computer setup inside. While it's not going to replace your desktop anytime soon, it should offer enough capabilities to allow for some for some dedicated functions, which you can either set up yourself or wait for some other companies to outfit the device with.
Onboard hardware includes an ARM-compliant 1.2 GHz CPU, 512MB of RAM and 512MB of flash storage. There are also connectors for USB and gigabit ethernet, which allows it to interface both with your home network and a wide variety of peripherals.
Already, many companies and DIY coders are looking at the Sheevaplug as a potential platform for home security (if you hook it up to a webcam or other accessory), a basic home computer (it can theoretically handle Web browsing, e-mail and music playback quite easily), a NAS controller (just add an external drive and network connection) and a host of other useful functions. If you can dream it up and it doesn't require a full-fledged computer, this thing can probably handle it easily.
If you're a programmer and have been looking for a project to busy yourself with, the $99 Marvell Sheevaplug Developer's Kit might be a good way to put those coding talents to good use. It nets you one unit of the super small computer, along with all the basic tools you need to get started playing around with it.