Welcome to the future of graphics processing technology. Today, NVIDIA released the next-generation Kepler series with their current flagship card, the GTX 680. Following along with this release, NVIDIA has introduced their new mobile offerings in the form of the GeForce 600M series. It consists of several rebrands along with a bunch of new Kepler goodness.
The top two offerings, the 675M and the 670M, are basically rebrands of the 580M and 570M. It's likely that NVIDIA will release a Kepler based 680M sometime in the future, but currently, the top Kepler based card is the 660M. The 640M has some confusing aspects surrounding it. It is offered in both a 40nm and 28nm variant with differing core counts under the same name. I'm not 100% sure on how these will be told apart in market.
Most of these chips will not see the light of day until manufacturers start shipping notebooks based upon Intel's upcoming Ivy Bridge, but NVIDIA notes that some of the offerings are already available in Sandy Bridge based notebooks. The list of notebook manufacturers using Nvidia graphics include Acer, Alienware, Asus, Dell, Gigabyte, HP, Lenovo, MSI, Samsung, Toshiba, and Vizio.