If you have a Discover credit card, you may be familiar with their Get More program. Through this program, each quarter you can earn 5% cash back in a particular spending category. From now until March 31, you can earn 5% back on airlines, cruises, hotels, and car rentals. I have to wonder if they chose this category because people aren't doing much spending in these categories right after the winter holiday, but since purchasing plane fare as far in advance as possible is often good idea anyway, this could be a great way to save 5% on an expensive purchase.
The only catch is that you have to actually sign up for the bonus each quarter--you won't earn the extra cash back automatically. To sign up, all you have to do is log in to your online account, click on "Cashback Bonus" in the righthand column, click on "Get More Program," and confirm your email address. If you don't access your account online, you can sign up for the program by calling customer service.
Also, you won't earn the bonus on more than $800 worth of purchases, which is a maximum of $40 cash back. You can further increase the value of your cash back award by choosing to redeem your reward with a retail partner that offers a bonus: a $25 gift card for Bath and Body Works in exchange for you $20 cash back bonus, for example, or my favorite, $40 at Enterprise Rent-A-Car.