I'm working on a larger-scope project right now that involves collecting a lot of sensor data with an Arduino to transmit over Bluetooth. For past projects, I've relied mostly on individually cut wires, but even if you use heat-shrink tubing or the like to bundle them up, they're still a pain to keep in order. Consumer electronics often use ribbon cables for this sort of thing when they can't just run traces on a board. I realized that I could make custom cables using the ribbon cables from old floppy and CD drives. With a steady hand and a utility knife, cut off the number of cables you need, cut them to length, and split and strip the ends. Voila -- custom-sized ribbon cables, and a great way to recycle old computer parts!