RC Arduino is a cool site that documents how to add an Arduino with gyro sensor to a RC car to make it more more controllable, basically "driving by wire", rather than directly, with the Arduino making sure it doesn't spin out.
"All of the throttle and steering commands in the car in the video are coming from an onboard Arduino. The Arduino is reading the incoming signals from an (drivers) RC Receiver and also a gyroscope within the car. It is using this information to assist the driver by controlling the yaw of the car under acceleration, braking and cornering."
There are some other cool Arduino-based RC car project there, too, so check it out.