I've been working with James Newton, of Linnistepper fame, on an open source commercial low cost closed loop motor conversion system. An encoder board is available for sale, along with a PIC based PID controller.

The relevant links are here:

Hakcaday.io project

https://hackaday.io/project/11418-massmindorg-abosoluteincremental-rotary-encoder

Purchase here!

http://techref.massmind.org/techref/io/sensor/pos/enc/ENC1.htm

http://techref.massmind.org/techref/io/servo/BOBPID.htm

This project may also be of interest to some of you. It is a low cost 40V 18A H bridge based on the same FET driver as my smaller servo drive project, with some easier to cool transistors.

https://hackaday.io/project/11419-massmindorg-40-v-15-a-output-dc-motor-drive