For dead flat black paint, believe it or not, I have been using Krylon Black Primer/Ultra-Flat.  Rattle can only, but it is as black as the monolith!  It dries very fast (usually <10 min) and shrinks a bit too, so if you put it on a little heavy, wait until it dries, all may not be lost (as long as you don't have sags or runs).

For black where decals need to be added, I use either ScaleCoat I or II (depending on whether the model is metal or plastic).  By the way, I use standard lacquer thinner with the ScaleCoat I and put it in a 200° oven for about 1/2 hour or so to dry.  Comes out looking like a new Steinway piano!

-- John