Memory makers revealed some of the first details of DDR4 at the MemCon conference in Tokyo. This new memory standard is expected to be introduced in 2012, with broad availability expected by 2015.
DDR4 modules are expected to feature frequencies of 1600MHz to 4266MHz, standard modules will use 1.2V, and low-power modules will require 1.1V or 1.05V.
More details and slides can be found at PC Watch, the site has some additional details about the new "Point to Point", which enables the processor to communicate with each module directly, and some info about the power consumption features. Also keep in mind that the DDR4 standard isn't expected to be finalized until sometime in 2011, a lot may change between now and then.