What DSLR cameras preform best at high ISO?

I've been into photography for quite a while and I really love it, but my current camera is very old(10 years) and limiting. I'm beyond ready to upgrade to something great. Because of the type of photography that I usually do, I'm looking for a camera that handles high ISO's very well. I'm only considering Nikon cameras, as that's what all my current gear is and I'm happy with it.
I know the D3/3s/4 are exceptional with high ISO performance, but I'm not sure I want to drop thousands of dollars on a camera body. I would certainly get my money's worth out of it, but it would take me quite a while to save up and be able to afford it.

What other Nikon cameras do very well with high ISOs?

When I last looked the Nikon D700 was the low-light champ. You ought to be able to get a low mileage body for $1, 500 or less.

The Nikon D800 and D600. The D800 is $2800 for the body only, and the D600 is $2000. They're hardly cheap, but are much more reasonable for someone who isn't a working pro than a $10, 000 D3. If you're looking for something even less expensive, the D7100 or D300S are very good for crop sensor cameras.

I'll second what the previous answer said. If the D3 is out of your range, the D700 is all but the same camera in terms of actual image quality. It shares the same innards, and it's full frame. The only differences are the burst rate and battery life, but on the other side the D700 has sensor cleaning and the D3 doesn't. Pair a D700 with a fast prime lens and you should have no trouble with the dark.

The newest full frame model (the D600) will probably do just as well, but I think it costs more than a used D700.

D7100 matches your criteria. It is best at handling high ISO. D7100 is a 24.1 MP DX-Format CMOS Digital SLR.
Here is a review of a professional photographer, i hope it will help your decision:

http://www.amazon.com/...5JFNSAJKX/

The D7100 has low noise, high ISO performance (1256 ISO)
It has 24.2 bits color depth and 13.7 EV dynamic range.
It has 51 focus points which Set focus accurately within the frame
15 cross type focus points Grab focus in difficult situations
It has a 24.0 MP resolution which Capture more than 30% more detail in your photos
It has a weather seal to shoot in the rain even (an edge for professionals)
D7100 has in camera HDR which Combines multiple exposures to capture high dynamic range
D7100 has a 2x faster max shutter speed but it does not have image stabilization sensor.

I hope it will be a perfect upgrade for a photographer.

If you can spend $2, 000, the D600 is what you want.

Here are a couple of ISO 25, 600 samples:

Be sure to look at the cropped image that shows the eye close up, which will be about 100% magnification on your screen.