UPDATE: I just changed the link, should be working now.
Receive 10% off your ENTIRE online purchase.
Offer Valid 07/26/2009 – 09/02/2009
For a Limited Time Only, receive 10% off purchases at Barnes & Noble.com. From classics to the newest titles in books, DVDs and CDs, you’ll find millions of exciting items. And remember, standard shipping is free on orders over $25.
Click here to get the offer. Use any American Express Card when making your purchase.
I’m actually not 100% sure you need to use an Amex when purchasing, though the offer is certainly being extended through American Express. You need to use your American Express when purchasing to get the 10% off, also this offer cannot be combined with your B&N Membership Discount (if you have one).