Today NVIDIA releases their new GeForce GTX 590 flagship which is based on two GTX 580 GPUs working on a single card. AMD released their dual-GPU HD 6990 design just two weeks ago, with power and heat being the decisive limit on performance it will be a tough fight between those cards.
Slow computer got you down? Maybe a hardware upgrade should be in your cards, if so this guide to the Fundamentals of Upgrading a PC is an invaluable read. PCSTATS Tips