DDR III is the name of the new DDR3 standard that's being developed as the successor to DDR2.
In February, 2005, Samsung Electronics announced a prototype 512 MByte DDR3 chip that will run at 1066 MHz (the same speed as the front side bus of the fastest Pentium 4 Extreme Edition, and around the speed of an Athlon 64's HyperTransport bus).
The memory comes with a promise of a power consumption reduction of 40% compared to current commercial DDR2 modules, due to DDR III's 80 nanometer technology, that allows for lower operating currents and voltages (1.5 V, compared to DDR2's 1.8 V or DDR's 2.5 V). Small, power-conserving devices such as notebooks could perhaps benefit from DDR III technology with extended battery life.
Theoretically, these modules could transfer data at the effective clockrate of 800-1067 MHz, compared to DDR2's current range of 500-667 MHz or DDR's range of 200-550 MHz.
The DDR3 specification is expected to be publicly available in mid 2006. Supposedly, Intel has preliminarily announced that they expect to be able to offer support for it near the end of 2007. AMD's roadmap indicates their own adoption of DDR3 will come in 2008.
The GDDR3 technology, with a familiar name but an entirely dissimilar technology, has been in use for quite some time now in high-end graphic cards such as the GeForce 6600 GT's and above, or the ATI Radeon X800's and above, and is used as main system memory on the Xbox 360.
Whilst many have claimed to have not noticed a significant difference, and raging debates exist on this topic, DDR3 is sure to set new performance benchmarks and increase speeds significantly.