Wire Clamps - we used padded hose clamps to hold the wiring in place. These are available in many sizes from LongAcre Racing.
Terminals - You'll need lots of terminals to connect to gauges, sensors, lights, etc. These can be purchased in variety packs from most of the online auto parts shops, although you're likely to find better prices at your local discount hardware store (Home Depot, Lowes, etc.) or at Radio Shack.
Wire - You'll probably need additional hookup wire. Having some 16-22 gauge hookup wire in various colors on hand will save you a lot of time.