In what devices are permanent magnets most commonly found?

There are 4 categories of Permanent Magnet applications:

Cat 1: The magnet's attraction or repelling force.
The simplest use of magnets.
A refrigerator magnet is a perfect example.
Compasses

Cat 2: The magnet's ability to convert electric force into mechanical force.
Electric motors are good examples of using magnets to convert electric energy into mechanical force.
A magnet is placed in a conductive substance, and then the magnetic field yielded by the magnet turns another piece of equipment, which rotates the motor rapidly.
Sound reproduction (speakers, headphones, etc.)

Cat 3: The magnet's ability to convert mechanical force into electric force.
Generators (even though in modern times generators tend to use electromagnets along with the permanent)
MRI machines
Accelerometers
Microphones
Etc

Cat 4: The magnet's ability to affect electron or ion beams.
Cathode-ray tubes, where the need to focus electrons uses permanent magnets for aiming purposes.