Just a day after NVIDIA unveiled full specifications and performance figures for its NV35 chip, ATI seems to be preparing a follow up to its R350 core used in the high end Radeon 9800 Pro and the RV350 (9600 Pro). According to this story at The Inquirer both chips have already taped out at TSMC and are expected to be distributed among partners by July.
Certainly I wouldn't expect new products based on these chips to be available at least for the next 3-4 months. ATI's current line consisting of Radeon 9800 Pro and 9600 boards are just becoming available to the public and in terms of performance and features they seem to be doing quite well (even if they're losing by a few points) against NVIDIA new chips.
Of course, now it would all depend on NVIDIA and the kind of pressure they are able to put on its competitor, if they manage to put out very optimized Detonators they could widen the performance margin in both, high-end and value targeted products.