D7000 or D300
How tough do you need your camera to be? Unless you're planning to shoot some action in Afghanistan the D7000 is plenty tough. Having said that, the D300 is tougher, if that's what you're after.
Also, it has better ergonomics - sits better in the hand - and is weather sealed. Finally, it has a larger buffer for continuous shooting as high speed.
However, the D7000 is more portable and strikes, for me anyway, the right balance between portability and function. Its high-ISO is superior to the D300's and, unless you're talking about the D300s, it has dual card slots. Its main weakness, in my opinion, is that it can't hold continuous shooting for long, i.e. its buffer is smaller than the D300/D300s. Otherwise, great camera, I switched from D300s to D7000.