Came up with a nice little hack with a Wii Nunchuk. The point of the project is to calculate the force of a swing of a Wii Nunchuk, using the built-in accelerometer, and output it on an LCD display. I found some useful information on starting the project here, including a handy hardware adapter to allow using the Nunchuk without cutting the USB cable (which I actually bought from Sparkfun). There's also download links to the library needed to interface between Arduino and Nunchuk via i2c.
I had to edit a couple of things in the library itself to get it working specifically to my application, but everything turned out really well. It's amazing how much you can learn just by seeking knowledge.