The current World of Warcraft release dates are as follows:
World of Warcraft - November 23, 2004
The Burning Crusade expansion - January 16, 2007
Wrath of the Lich King expansion - November 13, 2008
Cataclysm expansion December- 7, 2010
Blizzard has announced that they are doing a 4th expansion but haven’t released a date as of yet, more than likely the next release wont be till sometime late 2012.