Delta SkyMiles members who hold Delta-branded American Express cards can earn double miles or points (depending on the card) for charges made through Aug. 31. Holders of either the Delta SkyMiles credit card or the Delta SkyPoints credit card are eligible. Registration is required. Visit online or call 1-800-653-6051 to enroll a Delta SkyMiles card, or call 1-800-615-0403 to enroll a SkyPoints card. (P.S. Some carholders may be eligible for triple miles for everything)