Using cAVR hardware/protocol, a variety of input devices can be interfaced with the Hummer/DTV. There are several catagories of devices.
Analog Joysticks
A simple analog joystick consists of two potentiometers mechanically
coupled to a shaft. The POTs are wired as standard voltage dividers.
Test joystick was manufactured by Tandy (Radio Shack-- somehow appropriate given the Hummers' lineage), which had already been raided for parts (fire buttons.)
Accelerometer
An ADXL330 3-axis accelerometer was chosen for several reasons--
Although the ADXL330 runs only about $11 USD, I purchased a Sense-ADXL330 breakout board from Sparkfun.com. Ask me about that company sometime--they really stand behind what they sell. The first board was only partially functional, and they quickly send a replacement.
The Sense-ADXL330 board is $30 USD, but for me that's cheaper than making my own SMD pcb and buying the equipment for soldering, etc. They do sell the bare board for $5, if you're capable of that kind of work. Sparkfun's website has a cool tutorial for using an electric skillet as a heat-source for SMD circuits--well, maybe someday...