As per my experience Nvidia GeForce 6600 GT is good to use, and I came across some of the reviews, hope these will help.
http://reviews.cnet.com/graphics-cards/nvidia-geforce-6600-gt/4505-8902_7-31138497.html
http://ezinearticles.com/?Nvidia-Graphic-Card-Ge-Force-6600-GT-Review&id=333034