If you're looking for different forms of user input for your next Arduino-based project, one option is to use one of the several controllers available for the Nintendo Wii games console. Although such devices as the Nunchuk or Wii Motion Plus may seem complex, they communicate via the I2C bus which is perfect - as the Arduino can easily communicate with this data bus.
With that in mind several people have written an Arduino library, and one version has been forked by github user oldtopman, whose Arduino library makes it incredibly easy to get the sensor data from Nunchuk, Wii Motion Plus, and Classic Controllers. And if you don't want to cut the wires to your controller, small adaptor breakout boards are available from various resellers for damage-free connection.
If you're interested in experimenting with Arduino for your own inventions - but not sure how to learn - order one of our Experimenter's Kit for Arduino:
The package includes a wide variety of parts, sensors and modules including: a servo motor, lights, buttons, switches, sound, sensors, breadboard, wires and more. Furthermore a Freetronics Eleven Arduino-compatible board is included to make this an extensive hobby experimenter, inventor and starter kit.