I have heard good things about the ChevyDuty harness that Hedgehog mentioned, there are also several companies that make "street rod" harnesses with various circuits. Run a search on the archives, there was a recent discussion on the quality of various wiring harnesses.
Personally, I'm going to make my own harness, I can get any color wire with any color stripe from Waytek. It isn't the cheapest way to go, but since I'm building a TBI fuel-injected 250 for my truck, the harness is going to be weird.
