The next mainstream card from ATI will be the RV740, this card will compete against NVIDIA's GeForce 9600 GT. FUD Zilla claims this board will be released in the second half of 2008.
The new RV740 also brings a 256 bit memory interface and it is a 55 nanometre based chip made my TSMC. The 256 bit memory will move this mainstream card to the next level and will certainly mean that you will be able to set higher settings such as FSAA and Aniso.
We also know that it will be drastically faster than RV630 and RV635, but we wouldn’t expect anything less than that. Currently it looks like Nvidia will have a massive lead with its 9600GT, as the card is supposed to launch withing the next 10 days, while ATI's chip is scheduled for second half of 2008, probably in summer time.