Twenty-five Dollar Credit with an American Express Card at Amazon.com.

This has gone massively viral, but here it is.  Sign up here https://enroll.amexnetwork.com/US/en/Amazon/, and receive a twenty-five dollar credit when you spend seventy-five dollars or more at Amazon.com.  This works on gift cards too; it's what I did!

If you're interested in other offers, then make sure to "sync" a first-party American Express card, which includes Serve but excludes all other pre-paid, or a third-party American Express card (like from Bank of America or similar) at sync.americanexpress.com.

You can sync the card to Facebook and Twitter if you're interested in statement credits like the Amazon offer above.  Once you've synced, if you use Facebook, then you can just select the offers that look good to you at https://apps.facebook.com/amexlinklikelove/.  If you're using Twitter, then go to here https://twitter.com/AmericanExpress/favorites, look the list over, then tweet whatever offers that you like to @AmexSync.  For example, if I want to use Twitter to receive the Sony offer of a twenty-five dollar statement credit after a one hundred dollar purchase from store.sony.com, then I'd tweet @AmexSync #AmexSony.

Remember, you must sync your card FIRST at sync.americanexpress.com before selecting offers from Facebook or Twitter.

I think that the Facebook method is much easier, but even though many offers overlap, some are exclusive to just Facebook or just Twitter, unfortunately.