IMU (gyro + accelerometer) breakout board with integrated Kalman filtering?
I've worked on a project to implement the Kalman filter on an embedded system that was similar in hardware to the iNemo unit from STMicroelectronics.

Even if you can find these IMU (Inertial Measuring Unit) with 90% chance you will have to implement your algorithm by yourself; or if you're lucky, you can find someone that has the code. The problem is that this filter requires a lot of computation, and in our best experiment (using fixed point variables and trying to optimize the code) we were able to run it 45 times per second, in a STM32 at 72 MHz.

So maybe there is one, but as far as I know requires a good microcontroller or maybe a FPGA\ASIC.