I just got an email from southwest that they are having 1/2 price fares to vegas if you book today or tomorrow. Here's the info:
Fly roundtrip on a Wanna Get Away fare from any Southwest Airlines city to Las Vegas between January 13 and March 11, 2009. Sale fares available for purchase December 30 and 31, 2008 only. Travel January 13 through March 11, 2009.
enter promotion code LASVEGAS on southwest.com.