As stated the photographer makes the picture but there are a couple things you might consider. The first is the ISO to Noise ratio. The D90, D7k and D3 are better ones in the this catagory. Now before some D700 and D300 owners flame me, these are not my figures but from actual tests. You would still be fine with either of those cameras as well. I would also make sure you have a focus motor in the camera body so you can use all AF lenses and still auto focus.
You might want to look at the frames per second burst mode and see which one will work best for you. This will allow you take pictures quickly making sure you "get the shot"
The other two areas to think about is getting fast glass and at least a Class 10 card.