This tiny module can control two motors, 1 A peak each, and you can daisy-chain multiple units to control up to 62 motors with a single serial line. You can also order this controller including a color, printed manual, which is available as a PDF (292k pdf).
Documentation and other information
Pololu Serial Transmitter utility for Windows (Printable PDF: pololu_serial_transmitter.pdf)
A simple serial transmitter utility for Windows that lets you transmit sequences of bytes at a selectable baud rate to a selectable COM port. This program can be conveniently used to send commands to our serially controllable devices.
PIC-Based, Obstacle-Avoiding Robot (Printable PDF: pic_based_obstacle_avoiding_robot.pdf)
Sample robot project that shows how to use the Pololu micro dual serial motor controller with a PIC microcontroller.