Groupon offers a $10 Barnes & Noble Nook Credit for $6. That's a savings of $4 and the best deal we could find such a credit (outside of the deal below). The credit can be used on eBooks, newspapers, magazines, or comics. The credit must be redeemed by June 30. Deal ends March 30.
Of note, new users who download the NOOK app for iOS or Android can get a $5 Nook Credit for free. Deal ends March 30.