From the current Nikon line, I'd say the D600/610 provides the best value for the money. But overall, I think the discontinued D700 is the untimate in bang for the buck for Nikon bodies. The D700 really an unbeatable combination of features and price. I was fortunate enough to buy a mint D700 about a year ago with just 1,200 shutter activations, and use it as my backup body for my D3s.
Oh, and I think the D3s would be second on that list of best value! It's just an incredible camera.