At last. In the Fall of the Lich King content update (3.3),

At last. In the Fall of the Lich King content update (3.3), the great doors of Icecrown Citadel will be forced open. The mightiest heroes of the Horde and Alliance will confront and finally defeat Arthas, the Lich King -- but the lord of the Scourge will not easily part with his sword, his life, or his frozen kingdom.

This update includes an all-new raid and winged five-player dungeon; numerous interface improvements, including detailed quest tracking and instant cross-realm dungeons; scores of new quests and achievements; the epic tier-10 armor sets, and numerous class and system updates. You can find specific info, patch notes, and extensive details on all of the additions below.

The price of victory in Northrend grows higher with each passing day. Charge the gates, and bring an end to the wrath of the Lich King!