There was some speculation that DDR4 could be coming as early as next month, however this was set straight by the crucial twitter page, who said they expect it to be sometime next year.
DDR4 will feature 2x the speed of DDR3, 3x the density, and 20% lower voltage.
The lowest size available will be 4gb, the base clock speed will be 2133Mhz and there will be no more dual channel. Due to the increased density per module, the highest single stick of DDR4 ram available will be at 16gb, twice that of DDR3
Now, whilst this is great news for moving forward, I expect that the DDR4 prices will be very high at first release, and considering how DDR3 has actually become more expensive these last few months, DDR4 prices could be ridiculously expensive.