The Raspberry Pi is an inexpensive, single board computer that can be used in creative ways. raspberrypi.org
Here's a topic about all sorts of ideas for the Pi. Pideas.
Emulator
I think I may buy a Raspberry Pi, 2 USB NES controllers, and a 16GB SD card to make a sweet NES emulator that I can take with me anywhere.
I'd load all the good NES game ROMs on the SD card, then make a UI that can be operated with the D-pad and the A and B buttons that starts up once the Pi boots (just a game select screen, an alphabetical list)
then, I'd take two NES cartridges (SMB and Excitebike), and make a case out of them. (By cutting off the top of Excitebike and the bottom of SMB and gluing them back together so that you have one large hollow space to put the board in, then putting something in there to hold the board in place. I might have to the bottom of the case open up so that I can access the Pi. Anyway, you'd have all the ports exposed at the bottom or top of the carts so you could plug in controllers.)
I guess this is a pretty cool idea.