Wow, maybe I actually posted something useful!
Black is the most difficult color I've ever tried to take care of. My ex's H3 was black. I used Meguires waxes on it, and Meguires soap. I always liked the results, and they are reasonably priced and easy to find. Never tried most of what's recommended above.
My biggest word of advice is NEVER take the car to one of those washout bays at the local carwash. And if you really have to, DO NOT use the brush that foams. 2/5 times it will usually scratch the paint horribly.