Hall Effect Sensor:
Honeywell: SS495A? , Digi-key: 480-2005-ND SS495A.pdf
Magnets:
Rare Earth Magnet - Disc - D0.125 x T0.063
Magcraft: NSN0566
After some experimenting, a good distance is 3/8 inches between the two repelling planes.
-- SalomonTrujillo - 07 Aug 2006