Judging by their specifications and model numbers, the two chipsets seem to be re-branded versions of ATI's CrossFire Xpress 3200 and CrossFire Xpress 1600 (a.k.a. Radeon Xpress 200) chipsets. As their names indicate, the two chipsets are capable of running CrossFire multi-GPU setups. The 480X has two physical PCI Express x16 slots with eight lanes of bandwidth each, while the 580X sports two full PCIe x16 slots. Motherboard manufacturers including Asus, ECS, and MSI have already updated motherboard descriptions on their websites to account for the branding change.
Chipset naming aside, AMD also appears to have quietly introduced two new processors to its Athlon 64 X2 line. The company's price list on its U.S. website doesn't show any changes yet, but the one on the company's British site now lists new Athlon 64 X2 5400+ and Athlon 64 X2 5600+ processors. Both chips run at 2.8GHz, but the 5400+ model has 512KB of L2 cache per core and a $485 price tag, while its big brother has 1MB of L2 cache per core and costs $505. Oddly, the British price list also shows two Athlon 64 X2 5200+ processors with the exact same specifications and prices, while the U.S. page only shows one. If it's not simply an error, this duplication could suggest AMD is launching an Energy Efficient or 65nm flavor of the X2 5200+. Thanks to The Inquirer for the tip.