I got a few Mitsumi M28N-1 motors with built in encoders cheap off of ebay.

They seem to work ok, but unfortunately did not come with any pinout. It looks like the pins are layed out this way:

Mitusmi M28N-1 Pinout:
Blue (1): Motor A
Green (2): Motor B
Yellow (3): Encoder Voltage, 1.1 – 1.2V
Black (4): Encoder Ground
Red (5): Encoder Signal

I hooked up a resistor (~500 Ohms, selected at random) between the signal line and sensor ground.

The encoder power line seems to work if provided 10mA – 20mA, and quickly shorts and goes non conductive after that, so it looks like it is a LED with forward voltage around 1.2V. The signal line will be a square wave with frequency proportional to the spin rate, and magnitude a bit less than 400mV (probably will be a bit more or less depending on resistor value), testing with the datasheets rpm vs voltage chart shows the motor is fairly close to what is spec’d (will have table later)

In order for this to work as an interrupt input on my AVRs i will probably need to amplify and filter the signal a little bit, with a common emitter amplifier and a filter capacitor. Will look into that later. This brings up the point that many encoders may need signal conditioning, may want to make a board for that, not sure how to make it general on the H Bridge.