GPU Cafe claims NVIDIA is prepping the GeForce 9550 GT to compete against the ATI Radeon HD 4670:
Part two of the counter-attack is the 9550GT; going up against AMD's Radeon HD 4670. This product will be based on G94b, the 55nm version of the G94. This will still be 64 Shader processor part like the 9600GT but will feature a 192-bit bus width. In terms of die-size and bus width, AMD's 4670 will be cheaper to manufacture but might also end up short on the performance side of things.
In summary, both vendors will be looking to score in the sub $150 price segment. There will be good price/performance ratios from both sides. The only downside on Nvidia's product stack is that the GT2xx based mainstream/budget parts are still missing and lack the potential value from an OEM perspective.