RasPi Robot Board v2 by MonkMakes
The RaspiRobot Board V2 is an expansion board designed to turn your Raspberry Pi into a motor controller! This board comes fully assembled and includes a switched-mode power supply so you can supply your Raspberry Pi from a variety of battery packs.
The board fits right on top of your Pi's GPIO socket and allows for bi-directional control of both motors with an L293D H-Bridge motor driver chip. It also allows for control of both motor's speed independently and to use lower voltage motors than the voltage of your battery pack. The board can also supply the Raspberry Pi with up to 2 amps of power using a switch mode power supply, allowing you to run a fully-loaded Pi and the robot from 6xAA batteries (not included!)
For source code and support, check out the RasPi Robot Board v2 github page!