Geforce 8800GT for $120
or
Radeon 4850 for $160
+15%-20% performance for +30% cash.
The technique used for Anti-Aliasing in the Radeon is far superior to that of the now over a year old 8800GT which means you can crank those settings up to max and not suffer even close to the performance loss.
Also not to mention the Radeon supports the latest standards etc.
Going for new you want the Radeon, going for just better performance in WoW only, go for the Geforce, but get one used on E-bay for 50 bucks or something.
Hell if you really don't care I'll sell you my old Geforce 8800GT 512mb that has 2 months of use because I really feel it's a total waste to buy one brand new and right now it's just rotting in my basement in it's box.