3850 or the new 8800GT that will appear in a couple of weels with 256Mb or ram on it ... I can sense NVIDIA in panic mode.
3850 is also very economical on power ... at idle and under load.
Should OC quite well I imagine if you chose a good model / Manufacturer.
Methinks Saphire will have some competition as I imagine XFX etc will get on the superclocked wagon with these to push a range of price points in the very lucrative 130 - 170 buck range.
Good luck !!