Buy a graphic card

Hi all,
I have to buy a graphic card supporting CUDA for a new pc.
I can spent approximately 500$.
Do I have to buy the 8800 GTX or the 9800GX2.
Need advices :)

That depends on the other hardware you have. If your motherboard is PCI-E v2.0 then you can consider a 9800GX2 if not then I should recommend the 8800 GTX or maybe an dual or triple GT if you want to have compute capability 1.1