What would be the best video card for my computer?

You did not mention what your Power Supply Unit (PSU) is rated at. Most new vid cards are power hogs. Make sure you have a 400 watt or above PSU. You have a powerful system and I don't see a need for a better video card at the present time, unless you want to spend at least $150 for one from Amazon or Egghead. If you want, I would suggest an Nvidea 9600gt with on board ddr3 ram of 1 gig.