I found a tilt sensor, that works like a potentiometer: a mercury drop goes round and makes contact to a resistor. It is not damped, so if you punch it, you see a nice pendulum type of oscillation for some hundred milliseconds. Its approx 20mm dia, and 6mm wide and works for almost +/-90°. We use it to measure the tilt of sewer robots. Works fine, but costs approx 30$ each. Before we used linear magnetic types (a magnet as pendulum), size and form about the same as a 10000uF/25V Elko :), cost about 50$ have silicon oil damping a range of approx +/-45° but we got problems with the magnets of stronger motors. Of this type you also get open types which are smaller and cheaper. Here in switzerland PEWATRON sells both types.

Werner