Doe in a flurry, Nikon D3, ISO 1,000.

My regular digital camera is a Nikon D300. But it's in the shop for a repair, so Nikon sent me a D3 as a replacement. The D3 is a full-frame camera, as opposed to the 300, which has a 1.5 x crop factor. (In other words, a 400 mm becomes a 600mm.)
The D3 is also faster (shoots 9 frames per second) and can shoot at much lower light levels.
With the D300, you can shoot at ISO 800 and still get a very good photo.
With the D3, you can easily shoot at ISO 2500. At 3200, while the photos lose color saturation, but they have just a little grain. Problem is, the D3 is very heavy and I'm so used to my telephotos being 50 percent longer, that I'm not inclined to buy one. (Nikon has actually discontinued the D3, upgrading it to the D3s which reportedly has even better high ISO files and shoots 720p video.)
The D3s is a beast of a camera, too, so I probably won't buy one (it also costs $5,100).
So now what? Mebbe I'll wait for a better D300 with better high ISO files. Or mebbe I'll buy the Leica M9, the lightest weight full-frame digital camera being made today. That only costs $7,000. Ouch babe.