DDR3 isn't even mainstream yet and Qimonda is already making plans regarding DDR4 memory. German hardware site ComputerBase saw a slide at the Intel Developer Forum with Qimonda's low-voltage DDR3 and DDR4 memory roadmap.
Next year 1.5V/1.35V DDR3 modules with 1066/1333 clockspeeds will start getting mainstream with a shift towards 1.35V 1333MHz memory in 2012 and 1.35V 1600MHz modules in 2011.
The memory maker expects DDR4 will make an entry into the market around 2012, these chips will likely have a voltage of 1.2V and a frequency of 2133MHz. Five years from now the main memory will be 1.2V and 1.0V DDR4 modules with 2133/2667MHz frequencies.