Through June 6th, American Express is offering cardholders a one-time $20 statement credit on purchases of $20 or more made at Amazon.com.

Log in to your American Express online account and scroll down to Amex Offers & Benefits. Click "Add to Card" to activate it. Some cardholders may not receive all offers (YMMV), especially if you've received it in the past. Also, you generally need to be a cardholder in good standing for at least a few months to see these offers.