Three launch raids unlock December 9: Barrow Deeps, Hyjal Summit, Onyxia
Blizzard's raid overview says Barrow Deeps (10 players, 8 bosses), Hyjal Summit (20 players, 13 bosses) and Onyxia's Lair (40 players) open on December 9 for level 60 characters, all on weekly resets. Onyxia needs the Drakefire Amulet from a faction-specific attunement chain through Blackrock Depths and Blackrock Spire, and fire resistance is advised.
Source: Blizzard Entertainment, worldofwarcraft.blizzard.com