Well ATI had made the X600 which WAS supposed to be the equivelant but they pretty much screwed that one over as the 6600GT just completely destroys it. The only other alternative would probably be the X700, but even here:
^^lol, isn't the X600 on par with a 9600xt?? i think i remember seeing that in benchmarks. if that was suppposed to compete with a 6600gt, what a horrible failure