Southwest and Paypal have an offer for a $50 rebate when paying for a $250 or more ticket via the online payments service. It’s only valid through March 27 and only for the first 10,000 uses (there’s not actually a way to tell whether you’re one of the first 10,000).
As pointed out in this Flyertalk thread, even if you don’t currently have plans to fly Southwest, you could buy a ticket and cancel the reservation and then use the full credit towards a new ticket for travel within the next year.
(Hat tip to nsx.)