Arduino + $9 RC Car + $9 Parts = Programmable RC Car
Any RC car can be hacked and made programmable.
This project is great for electronics beginners and requires some soldering to build a simple Arduino shield used to control the car. Pulse width modulation (PWM) is used for speed control.
For full project details and a how-to guide: http://www.jbprojects.net/articles/programmable-rc