I am, as well, partial to the ATI. the 4850 and 4870s cars have some magnificant stats for the price.
For Nvidia i would stray away form any card with X600 or X500, at least currently.
The 8800 is more powerful than the 9600 and will blow away the 8600 (do NOT waste any money on a cheap card)
the 9800 is better than the 8800s in general but will cost more. I think the bang for buck will be the ATis or the 8800 GT 512mb.
check these out
ATI
Nvidia