Right now you can click here to go to Groupon and buy a $20 credit for Barnes and Noble for just $10! I did it a couple of hours ago and they've already emailed me my credit!
Here's the small print:
Expires Apr 10, 2011
Limit 1/person. Limit 1/trans. Valid in-store or online. Valid on sale items. Groupon value reduces by $10 on 4/11, except where prohibited. Groupon issued by Barnes & Noble Marketing Services LLC. See full terms.