I'm really excited to announce the latest board from the RRRF. It is the Magnetic Rotary Encoder v1.0 which allows you to measure rotational position of pretty much anything you want. At RepRap, we're using it to measure the speed and position of the DC motor on our extruder, basically turning it into an awesome and powerful multi-rotation Servo. The board itself uses the AS5040, which provides 10-bits of resolution per rotation (~0.35 degrees accuracy) and has 5 different output modes (quadruature, digital out via SPI, analog, PWM, and an Index pulse) It also has 6 different LEDs for fun and awesome diagnostics (or just to look cool, take your pick ;) To top it all off, it has 6 mounting holes, 2 of which are designed specifically for the great GM3 gearmotor from Solarbotics.
As always its 100% open source via the GPL. I'd specifically like to thank the guys who worked on the quadrature encoding page on the Playground, it helped me tremendously.