I believe that another poster may have suggested this before, but what about the first checked bag free to YX/F9 credit card holders?

DL and Amex announced this perk today, in connection with the Amex SkyMiles cards.

http://home3.americanexpress.com/cor...delta_free.asp

I believe that another carrier (Continental?) also offers this perk.

This would be a good way to retain or draw new business, as well as promote more business for the airline's credit card.