One of the latest Catalyst beta drivers confirms AMD is working on a GPU called R680:
"R680" = ati2mtag_RV630, PCIVEN_1002&DEV_950F
Few details are known about this chip but it's said that it will be launched in the first quarter of 2008 and will have PCI Express 2.0, DX 10.1, Double Precision FP, Quad Crossfire, UVD etc. It could be clocked at 800MHz or more and bundled with 512MB or 1GB of GDDR3 memory.
Source: VR Zone