Here is an interesting project that uses the Hall Effect to make a magnet hover in mid air. A microcontroller is used to make rapid adjustments in the strength of the electromagnet (the coil above) to center the permanent magnet and keep it still. Even with outside influences - in this case a poking finger (video below) - the permanent magnet quickly returns to to the center.
The first video below shows the magnet in action and being pushed around, the second gives a better look at the whole setup. Pretty neat.
Sources:
Project Page (translated) via Hacked Gadgets
