The D90 is alright, but the D90 lenses are the proprietary ones, aren't they (only useful for the 50 and a couple others, right?).
G2G, any chance you would want a nice used one? It's hard to beat a D300 or better. You're welcome to play with mine anytime you like. All the pictures I took at the full auto shoot were with it.
Proprietary? First I heard. The 90 has an internal af motor, should be able to take any nikon compatible lens (nikkor tamron etc)