After seeing Mecanum wheels in action, I wanted to give them a try. I initially tried Fingertech Mecanum wheels but soon switch to Vex wheels.
A Parallax Propeller QuickStart board reads the four sets of quadrature encoders and the signals from the RC receiver. Using these inputs the Propeller microcontroller computes the power levels to send to the four motors.
I usually use as more of a RC toy than a real "robot" since it's not often autonomous. I have had to drive several figure 8's while autonomous.
Here's a video of the robot in action. Sorry about talking so much before I start demonstrating the robot. The robot doesn't start moving until near the 2:00 mark.