We are just finishing up testing on the first batch of Mongoose IMUs. We've combined an Atmega328P with a ADXL345 accelerometer, ITG-3200 gyro, HMC5883L magnetometer, and BMP085 barometer into a small board.
We took the AHRS firmware writen by Jordi Munoz and updated it to work with the new sensor and have it outputting RPY as well as all the raw sensor data at 50Hz.
The exciting thing about this design is that there are 9 extra IO pins that come out to a header, so you can add servos, or a GPS for example.
I have some pictures and more info up on the blog.