It will be the GeForce 8400 GS, according to VR Zone. This card uses the G86 core like the GeForce 8500 GS but will have a 64-bit memory interface.
Just like the GeForce 8500 GS this new card will have a 450MHz core with 400MHz memory.
The price will be only $45, which makes it a Radeon HD 2400 Pro competitor but according to rumours the GeForce 8400 GS will offer better performance.