We use Powerwerx zip wire for long runs that we want the power/ground to stay together. It's not the most flexible wire for tight bends, but it routes straight lines very cleanly.
http://www.powerwerx.com/wire-cable/red-black-zip-cord.html
For electrical board wiring, we use high strand count silicone wire which allows for much a much smaller bend radius than the zip wire. This is more expensive, so we use it sparingly.
http://www.buddyrc.com/accessory/silicone-wires.html
Hope that helps!