Today only, use coupon code FB2012 to get $10 off a Wanna Get Away Fare on Southwest! This is one of the first free use coupon codes I have seen that are good on the cheaper fares to begin with.
Your flights must be between February 21and March 15 to qualify.
You might be able to purchase two one-way tickets and use the coupon code twice. Not sure if they will allow that. But it is worth a shot right?