nForce4, the basic value chipset for 939 and 754, should be found in Socket 754 and low-end Socket 939 boards. Although this is the budget member of the family, still expect to see the RAID and gigabyte Ethernet features mentioned above, as well as much more.
nForce4 Ultra, will sell in the $100 to $150 price range, and has the additional benefits of an unlocked 1000 Hyper Transport, support for 3Gb/s SATA drives, and nVidia's secure networking engine, which is called ActiveArmor.
Finally, nForce4 SLI, is the high end version, and will sell for $150 or more. This member of the family is the only version to support programmable PCI Express lanes, which makes dual video cards a possibility.