American Express is offering cardmembers 5 free iTunes songs if they register online and then use that same card to buy 5 song downloads from Apple iTunes. The limit appears to be purely on a per card basis.
Thanks for reader Nick for the tip. See the fine print:
To be eligible to receive the statement credit, you must register any valid U.S. American Express® Consumer Card or Business Card from American Express OPEN at amexnetwork.com/iTunes and use that Card to make a purchase on iTunes® between 2/10/11 and 3/15/11. A statement credit equivalent to the price of 5 song downloads on iTunes plus sales tax will be issued generally within 5 business days after your qualifying purchase, but may take up to 2 billing periods to post to your account. Limit one statement credit per registered Card regardless of the number of transactions made. If your registered Card is replaced, you must re-enroll the replacement Card prior to making the iTunes purchase to get the statement credit. Additional terms apply; see Registration Terms and Conditions for details.