Qimonda, the awkward brand name of Infineon, is working on some interesting graphics memory. You can already buy a Geforce 8800 with memory clocked at 2.3 GHz.
The real 1.2 GHz or 2.4 GHz effectively memory is coming soon, sometime this year. Obviously many graphics card manufacturers wants to stick with DDR3 for a while, before they move to DDR4.
This memory has 256 to 512 Mbit density and bandwidth up to 9.6 Gbytes/s and it comes packaged in FBGA-136.
You can find more details here.