Delta is giving $50 dollar Amex Prepaid card back for selected roundtrip purchased with ANY AMEX credit card.
Here is the detail
* Register for this offer
* Book and purchase a round-trip, nonstop flight between New York/JFK and Los Angeles, San Francisco, San Diego, Portland or Seattle at delta.com with any American Express® Card
* Complete travel from May 1 to June 30, 2008
This is no limit for the number of card you can get.