The Inq writes NVIDIA is working on the G98 GPU, which will be launched for about $199 within a couple of months:
The answer is short and sweet. G98 is the new mainstream part with enhanced and more wide memory controller, going head to head with ATi's own RV670. G98 is all that G83 (8600) was supposed to be, but failed to deliver.
A while ago, a rumour about GeForce 8600 with 256-bit controller appeared on the market. That part is no other but the G98, even though the GF8600+256-bit is a bit downplayed, G98 is significantly faster and has much more shader power.