Targeted Amex cardholders can earn an additional 2% cash back on airfare purchased online from April 1 to May 31, 2008. This rebate is in addition to any that you would normally earn with your card. This extra cash rebate will be awarded on up to $25,000 in qualifying purchases, for a maximum extra rebate of $500. You must enroll by May 31 and some restrictions do apply.

If you are eligible, you can either enroll online or via phone by calling 1-800-794-1308 and using promo code 110890002. (Via FW).