On a lot of black guys I've always liked the one length close crop - not shaved, but close. Looks really crisp and neat. But it does depend on your face shape.
I Googed Ludacris's hair and it looks like right now he's wearing a very short low fade, which is a really good style I think. The sideburn style is f'ing awesome, if you have enough facial hair to work with, but even without that the haircut works.