Watch evreward or one of the other tracking portals. Think right now the best offers are 20X through United mileageplusshopping.com (maybe with some other bonus miles for Chase United card holders) and 15X for aadvantageshopping but just recently one of the biggiest (FTD, 1-800-flowers etc) was offering 30X. Go to evreward.com, click browse, click florists, click on the top of the rebate column to sort by that.