Vex Robotics Optical Shaft Encoder Kit

Excellent for general needs. Using them on telescopes.They are not high-performance PPR but they track very well (no missed pulses).With Gear Ratio of 4:1 and quadrature, the resulting resolution is 0.25 deg.No resistor pull-up/pull-down needed for Arduino and/or Atmel chips. I do recommend interrupts for fast response.

The optical shaft encoders work great for programming your robot for autonomous mode. They are super easy to use. Do note that each unit requires 2 ports on the microcontroller unless you want to write code to read input with only one cable (you will lose the ability to determine direction however)

It's incredibly inexpensive. I didn't use it for the intended line of products so the plastic got marred quite easily. There are some overhanging chips but they were easily broken off by using a metal shaft.

I didn't use these with other VEX components but they worked fine for my purpose. Easy to connect with the three pin connectors.