It is now official! The expansion for WoW will be called The Burning Crusade. Details were announced today at BlizzCon and are available on the new website for it (linked in the article below).

World of Warcraft: The Burning Crusade Announced!
Blizzard is proud to officially announce our upcoming World of Warcraft expansion set, World of Warcraft: The Burning Crusade! Join the Horde as one of the power-driven Blood Elves, or aid the Alliance as a yet-unrevealed new race! Explore the scarred Orcish homeland of Draenor! Delve into mysterious new dungeons, engage your enemies on new battlegrounds, and acquire wondrous new items! Take up dangerous and rewarding new quests for your faction! Train in an all-new profession! Increase your might as an adventurer up to the new level cap of 70, with new spells, abilities, and talents, and meet head on the plethora of new challenges awaiting you!
We will be revealing new information about the expansion set, including the identity of the new Alliance race, as the release draws closer. Be sure to visit our new expansion site for the latest updates! Read the press release.