Any advice on buying my first professional Nikon?

I'm looking to spend between 700 and maybe up to about 1100. Has to be a Nikon, I already have all their lenses. I don't need to do video, only photos. I've been working as a wedding photographer, sometimes I need to blow things up kinda large, maybe at a max of 20" by 20". I've been looking at the d90 and d200 quite a bit. Also I don't mind buying a reasonably priced used camera if there's any especially good sites for it.