A very simple and elegant non-contact switching mechanism,which can support currents upto 1.2A (but look into datasheets for part specific values).
The device consists of 2 ferromagnetic contacts,parallel and overhanging,encased in a glass case(much like diodes are.) They range in length from 2.0 inches long to as small as 0.025 inches long.When the device is in proximity of a magnet, the two ferrous contacts inside the switch pull together and the switch closes.So,not terribly great switching times(~1mS),but useful nonetheless.
Theres an app note and working description at Sparkfun,click here to read it.(PDF) They also have it in the catalog(here),and can be purchased for $1.50 a piece.
Common applications include sensors and alarms.They can also be used for checking orientation of various objects(which have some magnet attached,so proximity would turn on the switch) etc.
A very detailed writeup on them,at http://reed-switch-info.com/.