An adjustable potentiometer can open up many interesting user interfaces. Turn the pot and the resistance changes. Connect VCC to an outer pin, GND to the other, and the center pin will have a voltage that varies from 0 to VCC depending on the rotation of the pot. Hook the center pin to an ADC on a microcontroller and get a variable input from the user!
This is a center-tap linear type potentiometer. The outer two pins will always show 10K resistance, the center pin resistance to one of the outer pins will vary from 10K Ohm to about 50 Ohm. The pot is linear meaning the resistance will vary linearly with its position. This is a good choice for general user interfaces.
This pot works great in a breadboard but on a few breadboards, you may have to trim off the large metal anchors.