With NVIDIA working diligently on the GT300 series GPUs, it should come as no surprise that AMD is wanting to get some DX11 cards out by the end of the year to provide some sort of competition.
Now it looks like AMD will have at least three new cards out before the year is up. First up will be the single GPU RV870 card, followed by the dual GPU RV800. These two cards will take care of AMD's performance offerings. AMD is also planning on bringing the mid-range RV840 GPU around the same time as well. There will also be the RV810 chip for the low-end market, however it is not certain that AMD will have it available before the year is up.
Assuming that AMD follows its current naming scheme, these should become the Radeon HD 5000 series cards. RV870 should become the Radeon HD 5870, RV800 the Radeon HD 5870X2, and RV840 as the Radeon HD 5850.