The OceanServer Serial 3 Axis Tiny Digital Compass is even smaller than the WiTilt and packs in a high resolution digital compass. This board is only one inch square, hoever it has a serial output rather than a wireless one, but there are a number of solutions to turn this into Class 1 Bluetooth (100m) -such as

BlueConsole
The Brainbox adaptors or the
Air Cables which have solutions for up to 10KM's

There are other sensor options in this range including the:

IMU 5 Degrees of Freedom sensor, which would need a wireless card and driver, but it carries a IDG300 dual-axis gyroscope and Analog Devices triple axis accelerometer and is less than 1 inch square - Dimensions: 0.75"x0.9" (20x23mm).

Rather more expensive is this Complete Inertia Measurement System - IMU 6 Degrees of Freedom - v2 with ADXRS150 which also does not include Bluetooth. Dimensions: 2x2" (51x51mm)