According to [H]ard OCP, Nvidia is planning to release four new 9xxx graphic cards during the first half of 2008.
Around February/March 2008, GeForce 9800 GX2 will be released. This card is meant to replace Nvidia's current top performer, the GeForce 8800 ultra, as it would be "at least 30% faster".
GeForce 9800 GX2 can be easily described as two 8800 GPUs with 65 nm die and connected together through an internal SLI link.
During the same February/March 2008 timeframe, Nvidia will also release GeForce 9800 GTX which is meant to replace GeForce 8800 GTX. Little is known about this card, but we know that it will support triple SLI.
About a month later, Nvidia will release GeForce 9800 GT but we know nothing about this card yet.
Later during 2008, GeForce 9600 GT will be released. This card should fall below GeForce 8800 GT, but outperform GeForce 8600 GTS. It should retail for $169.
All 9xxx are based on Nvidia's current 8xxx offerings. The 9xxx naming only suggests the die shrinkage to 65nm.