Opening ceremonies have taken place at Blizzcon and here are the important notes for the Wrath of the Lich King expansion

The continent of Northrend in Azeroth will be unveiled, and supposedly “threaten all life on azeroth — scourge”
Level cap raised to 80
Exciting new abilities and new talents for all classes
New battlegrounds
Siege weapons
New Profession: Inscription, which will allow you to permanently enhance spells and abilities
The ability to change the appearance of your characters
Death Knight Hero Class being introduced
New Dungeons, Monsters, and Items
In addition, there are several new items currently under development to be released via patch:

Integrated Voice Chat
Guild Banks with full logging features for deposits and withdrawals
Orc shoulderpads will be fixed
New 10 man raid instance, Zul’Aman will be in Ghostlands
Stay tuned as we bring you more info!