R600 is supposed to come out next month, this is their direct fire back at Nvidia's 8 series.
I believe the one that will beat a 8800GTX is called an X2900XTX or something. I can't remember now though.
Then the one that will fire back at Nvidia's 8900GTX when they release it is an X2900XTX2 which is just like the 7900GX and 7950GX having two chips on one card.