I'd go against the trend

and say either a d7k (newer model) or d300(s)/d90 used.
d300 (several on the for sale bit) are going for around 500.
As for lenses, if you like prime, try the 35mm f1.8g (either on the suggested camera or your current one) around 180ukp (possibly less if you look around a bit) or used.
It is a nice lens although I seem to still be getting missed focus :/
If you did go for the older d300/s type camera, you could look at a 50mm f1.4d (around 200ukp new .. probably 150 used?)
Depends if you've used primes or are more happy to use zoom...
(I've heard there is a tamron 17-55 I think f2.8? meant to be very nice).
Pics to the ones I've taken in the signature.
Good hunting!
Edit: Thats assuming you want to stay with nikon - might be best to pop to a camera store and handle as many as you can or go to a local camera meet?