Cheap-O (the sub $2 magnetic endstop)

This is the simplified DIY version of a magnetic endstop. Instead of using a hall effect sensor and some logic, it uses a hall switch. So the board is much simpler.
PLUS - it has a control LED.

Cheap-O in action: http://www.youtube.com/watch?v=smRay_nAUWA

Update: Improved STL for super slim design.