My 6800GT 256mb has held up well since I got it in September 2004 for
$350 (which was a pretty good deal at the time), and I don't plan to replace it until perhaps September 2007 or later, and then really only because it's AGP.
Admittedly, I don't play highly demanding games on it - WoW and Half Life 2 are the main ones right now, albeit at 1600x1200.
Before that I had the 9700 Pro AIW, which I recently gave to a friend so she could play WoW better than with her GeForce FX 5200
I'd probably vote for the 9700 Pro, because it was much more affordable than the 6800GT even though it was top of the line in its day.