A company called Robolytics, a sponsor of teams 2337 and 1684 based in Lapeer, MI, designed a product called iAMdriver which essentially replaces the cRIO on a FIRST robot and allows the robot to be driven by an Apple iDevice (iPad, iPhone, iPod Touch). It's a rather inexpensive and very user-friendly system to use: the accelerometer on the device is used to drive the robot by holding the device flat and tilting it to control. Also, there are controls for both digital and analog outputs on the interface for the proprietary (free) iDevice application.
The device is distributed by AndyMark and can be found on their website
here. It's a great system to use for robot demonstrations where the intent is to allow people not involved with FIRST to drive a team's robot. Instead of spending ten minutes explaining controls, you can hand someone an iPhone/iPad/iPod, tell them "Tilt to drive" and spend that ten minutes pitching FIRST and FRC.
My apologies if this sounds like a sales pitch: it *is* after all something that our team takes a lot of pride in, and that I personally find great fun to use.
I know that there are other similar systems that perform similar functions, though. The uCANDrive, a similar system designed by Cross The Road Electronics, uses an Android app to control CAN hardware. I suppose I could talk this up, too, but lack of familiarity and willingness to elaborate is a good recipe for a sticky situation O.o