This ratiometric linear Hall-effect sensor provides a voltage output that is proportional to the applied magnetic field.
This is a very simple breakout board for the popular HMC6352.
This Melexis US5881LUA (flat TO-92 package) magnetic sensor features a low sensitivity, unipolar design, meaning that it won't be affected by earth's magnetic field, and only responds to a change in one polarity. This particular model responds only to a South-pole magnetic field.
The HM55B Compass Module is a dual axis field sensor that works by reading the earth’s magnetic field and determine the direction.