i think a 7800gtx should fit the budget.
I'd actually go with a Geforce 6200 IF you have the money. for its price, its a good card on its own, but if you OC it (which you can alot) then its alot better...if you're lucky, you can softmod it to a 6600 (which is awesome). plus it has Shader model 3.0...you really can't go wrong with it if you're on a budget