Implementing my own ESC (electronic speed controller)?
Here is an introduction to electronic speed control systems: http://www.stefanv.com/electronics/escprimer.html

Actual design depends on the type of motor you want to drive. A 300A high-torque gear motor is much different from those tiny featherweight propeller motors. At the heavy-duty end of the scale (300A) is something like this: Open Source Motor Control. All designs are online and there are a few articles explaining what the heck is going on. At the other end of the scale are small prop motors, like those in the MikroKopter.