If ever you were interested in World of Warcraft, there is no better time to start than now. As of this writing, Amazon is having a sale where you can get both the World of Warcraft Battle Chest (which includes the original game and the Burning Crusade expansion) and the Wrath of the Lich King expansion for $20 each. That will get you caught up with everything except the new expansion, Cataclysm, for only $40. That’s half of what it would usually cost.
On top of that, Cataclysm is basically introducing an entirely new world to explore and level in by reshaping the face of what has been there for the last six years, so, as far as stuff in-game goes, it is also a great time to take the leap if you’ve been considering it.