HardOCP has some information on the next-generation nForce 500 series AMD platform from NVIDIA. This will be launched around the same time as AMD's Athlon 64 Socket AM2 processors and will feature the chipset codenamed MCP55:
It will be marketed from low to high end market, such as exclusively low-end nForce 550 (MCP55S), nForce 570 for mainstream (MCP55-Ultra), supporting SLI technology with nForce 570SLi (MCP55P) and dual x16, high-end SLi nForce 590SLi (C51XE + MCP55 XE). nForce 590 SLi will be designed and improved with overclocking enthusiasts’ demand.”
The nForce 590 SLi will have Dual x16 PCI-Express and will have an internal design with a higher standard than AMD's normal spec. According to the site the chipset can be overclocked massively without increasing the voltage.
There's also information on NVIDIA's Tritium platform, which will be something like Intel's Centrino or VIIV platform:
When “Tritium” MCP chipset used in with a “Tritium” GPU, north bridge, south bridge and PCI-E’s operating clock will be 1.3 times higher, or more, than normal spec, this will provide higher data transfer rate. Currently, we know only nForce 590 SLi can be certified for Tritium MCP, GPU spec has yet to be released. On a side note, a famous overclocking memory manufacturer told us, that nVidia also suggested Tritium DIMM concept: if memory manufacturer passed the Tritium and compatibility test, then the overclocking performance as well as the compatibility is guarantied when used on Tritium platform.”