The first you can see at Expreview; it is the 55nm process GTX280 renamed the GTX285. Along with the smaller process it sports a new PCB design, thankfully no longer than the original and a GPU that has been bumped in speed by an indeterminate amount. It will also sport 1GB of GDDR3. The new process carries one big advantage, the maximum power has been reduced to 183W from 236W, perhaps allowing a bit more leeway in overclocking before temperature becomes a problem.
There is also a direct competitor to the HD4870 X2, the GTX 295 that will sport a pair of 55nm GPUs, 480 shader processors and have a 289W TDP. It will support Quad SLI and offers 2 DVI and 1 Display Port as outputs, HDMI will most likely be supported via an adapter. You can see several sets of pictures of this card at VR-Zone, but you will have to wait for CES 2009 (or a leak) before we know the exact frequencies this card will run at.