Hi shadow,
The easiest way of electronically controlling the power feed to a motor is via solid-state thyristor devices such as SCRs or triacs. I'm giving you a simple ckt built around a SCR. Control element is SCR which feeds 1/2 power to the motor (this results in only a 20% or so reduction in maximum available speed/power), but in the off 1/2 cycles the back emf of the motor is sensed by the SCR & used to give auto adjustment of the next gating pulse,to give auto speed regulation. I do not know what your requirement is but this ckt provides a high torque under low speed conditions. Hope this will help you