AMD have launched their Radeon HD 7970 next-generation GPU today, and the reviews seem to be loving it. As a single-GPU card, it performs amazingly, and can actually keep up with the dual-GPU Radeon HD 6990 and NVIDIA GeForce GTX 590. There are plenty of reviews to check out, and one CrossFire review which got my blood pumping.
AMD's GCN is featured, Graphics Core Next, which is built on a 28nm process. The Radeon HD 7970 is now the fastest single-GPU in the world and does a damn good job punching the dual-GPUs square in the nuts, too.