I am currently using three Pi’s to automate my home, home theater (XBMC), and one for several unfinished experiments.

The Raspberry Pi is a credit-card sized computer that plugs into your TV and a keyboard. It is a capable little computer which can be used in electronics projects, and for many of the things that your desktop PC does, like spreadsheets, word-processing and games. It also plays high-definition video. We want to see it being used by kids all over the world to learn how computers work, how to manipulate the electronic world around them, and how to program.

http://www.raspberrypi.org/

Links

Pi for Java, a library for using the GPIO from Java.
http://pi4j.com/

Swedish webshop selling Pi’s and other things you may need when tinkering with your R-Pi.
http://www.r-pi.se/