At this year's BlizzCon celebration, Blizzard revealed that the long-awaited StarCraft II is being broken up into three full-length games. The first, StarCraft II: Wings of Liberty, follows the Terrans, and will likely hit sometime early next year. Heart of the Swarm and Legacy of the Void follow the Zerg and the Protoss, respectively, and will ship at roughly one-year intervals after WoL. Blizzard says owners of the first part will be able to play all factions in multiplayer, and the second and third parts are basically expansion packs, though it's not yet certain whether they'll be stand-alone or not.
Each will feature new single-player content, including a unique meta-game, since the Terran model that has Jim Raynor cruising around the galaxy choosing missions wouldn't suit the Zerg or the Protoss.