In a repeat of an offer from last fall, Delta is offering 5000 bonus miles for transferring the equivalent of 20,000 Skymiles into a Delta account from a partner (e.g. Diners Club, American Express Membership Rewards, various hotel programs).
Registration is required. The promotion lasts until August 31st and the bonus can be earned twice.
If you transfer American Express Membership Rewards points before July 15th, this offer should be stackable with the 15% percent transfer bonus as well.
Update: The Membership Rewards double dip may not work, as Amex isn’t explicitly listed as a transfer partner for this offer. Strange.