My new Sony a700 has the ability to shoot at ISO6400. It pretty amazing because my a100 could barely shoot at ISO800 without CRAZY digital noise, and it maxed out at 1600, but the images were not usable at all.
Here are two pics of my pets that I took tonight at 6400.
Without flash, at night, lighting source was my deck light:
This is my cat, no flash- lighting source was my dining room light.
Both were shot with a Sony a700 with a Minolta 80-200 f2.8 Lens at 200mm.