The high-end model is called Tahiti, it will arrive in a Pro and XT edition, while the enthusiast-class New Zealand is based on two Tahiti GPUs.
Details about the other chips are less certain. Thames is possibly a low-cost mobile chip or a performance edition, which will arrive in three versions: LE, Pro and XT/GL.
The fourth chip is Lombok, this GPU is planned in Pro, XT, AIO and XL GL variants. The codenames suggest this could be a desktop performance chip.
The launch of these cards is expected by Q4 2011.