According to information from the site 4gamer who put their hands on a roadmap of AMD (see below), the next generation of AMD GPUs would be known by the code name Southern Islands. Presumably the name of commercial graphics cards will be declined if AMD continues to name its products with the same logic, Radeon HD 6000.
Range Southern Islands (southern islands) would be broken down into five GPU (whose code names are names of islands):
Caicos planned for late 2010 which would be the successor of Cedar (Radeon HD5450)
Turks planned for late 2010 which would be the successor of Redwood (HD55xx/HD5670)
Barts scheduled for early 2011 would be the successor of Juniper (Radeon HD57xx)
Cayman planned for early 2011 which would be the successor of Cypress (Radeon HD58xx)
Caribbean scheduled for early 2011 would be the successor of Hemlock (Radeon HD5970)
This whole new range of GPUs Southern Island would be engraved in 40nm and AMD would focus on the tessellation to catch up on Nvidia cards and Fermi.

Radeon HD 6000 Series