I have recently started work prototyping some ideas for a simple wireless remote controller for my robots.
Originally I was going to purchase some thumb joysticks available from Sparkfun to use for prototyping. Luckily I had the idea to use an old Playstation One Dual Shock controller that has been collecting dust for ages in my closet. It was kind enough to donate its innards for my purposes. Surprisingly the thumb sticks found inside the Playstaion controller are identical to the Sparkfun ones.
I went ahead and etched two breakout boards for the liberated thumb joysticks and have begun to interface them with one of my ATMEGA168 breakout boards. The software is really quite simplistic. It is just a matter of doing two analog to digital conversions for each axis of the joystick, forming a packet with the joystick readings and transmitting the packet out the micro's USART to the Xbee module.