Do this now: Amazon.com credit from American Express

Hot on the heels of Small Business Saturday, American Express is offering another deal that you'd be crazy not to take advantage of: a $25 statement credit when you spend $75 or more by December 31, 2013, at Amazon.com on each American Express card you carry.

There are lots of ways to enroll in the promotion, including "syncing" your cards through Twitter or "adding the offer" to your card through your online banking account. The easiest, however, is to go to this page and enter your information for each unique American Express number you have.

Unfortunately it isn't possible to register for the promotion through multiple channels and earn more than 1 $25 statement credit: after "adding the offer" to my account online I wasn't able to then register through the promotion site.

On the plus side, while most of American Express's prepaid cards (like Bluebird) are not eligible for the promotion, Serve (the Bluebird-lite prepaid card product) is eligible. So if you or someone you know still has a Serve account, be sure to register that as well.