That's a pretty solid system, so. . .
IMO, graphics cards are one of the areas you really get what you pay for. You could argue back and forth for hours on which brand was better, but you buy a high end AGP card, and you had a crappy one before, you are gonna be happy. Regardless. Here is a good site outlining chipset specs
. It all really comes down to what you can afford. The ones that cost a lot, cost a lot for a reason.