Although you may not see PS/2 keyboards & mice as often on desktop computers, there's still tons of them out there, and they're really easy to interface to a microcontroller. PS/2 devices are powered by 5V and use two data pins to communicate back and forth. There's tons of example code out there for every kind of microcontoller (including Arduinos) for keyboard and mouse interfacing.
So all you need to do is connect from the PS/2 plug to your breadboard. Unfortunately, these plugs are not breadboard friendly. That's why we really dig this connector. It's sturdy and easy to panel mount, and has pre-soldered wires connected to the 6 contacts (of which 4 are used). We thought it very nice and easy to use!
For PS/2 devices: