Using one serial output from the BASIC Stamp module, this motor controller can independently set each motor to go forward or backward at any of 127 speeds. To control additional motors, you can connect multiple motor controllers to the same serial line. The Pololu controller supports a low range of voltages and comes pre-assembled. It measures only .9 x .45 inches and is compatible with all BASIC Stamp microcontrollers. In addition to the Pololu controller, you will need a BASIC Stamp module, programming board and motor(s).

Downloads:
Pololu Micro Dual Serial Motor Controller Documentation (.pdf)