The 6600GT is pretty good for the money.
I actually have a spare, unused 6600GT PCI Express I got from Newegg on accident a week ago. I thought it was an AGP card until I opened the box and realized my mistake. Newegg wants to charge me a 15% restocking fee, so I'm probably either going to sell it on eBay for what I paid for it: $190. If you're interested, let me know -- you might save a little on tax and shipping. My email address is chrismichaelgardner@yahoo.