To celebrate the 30th Anniversary of the invention of MIDI they're carrying these handy 5-pin MIDI jacks. They're what you see on the back of nearly every synthesizer and drum machine. These are nice sturdy jacks, and breadboard-friendly, with all the pins on 0.1" spacing for easy wiring.
This handy tutorial and wiring diagram will show you how to easily turn your Arduino into a MIDI controller!
Also compatible with DINSYNC cables, if you have a really old drum machine!