Update: Wrath of the Lich King is now official. Check out the official site at the link below.
Here's a bit more about it from Blizzard's site:
The Lich King Arthas has set in motion events that could lead to the extinction of all life on Azeroth. With the armies of the undead and the necromantic power of the plague threatening to sweep across the land, only the mightiest heroes can oppose the Lich King's will and end his reign of terror for all time.
Blizzard Entertainment's latest expansion to World of Warcraft – Wrath of the Lich King – adds a host of epic content to the existing game world. Players will achieve soaring levels of power, explore a vast new continent, and battle other high-level heroes to determine the fate of Azeroth. As you pit yourself against the dangers of the north, prepare to:
-Master the necromantic powers of the Death Knight - World of Warcraft's first Hero class.
-Quest to level 80, gaining potent new abilities and talents along the way.
-Learn the craft of spell augmentation with the new Inscription profession.
- Brave the harsh new continent of Northrend, the icy domain of the Lich King.
- Engage in epic siege warfare, deploying mighty siege engines to lay waste to destructible buildings in your path.
- Transform your hero's look with new character-customization options, including new hairstyles and dances.
- Explore perilous new dungeons filled with some of the deadliest creatures -- and greatest treasures -- on Azeroth.