It seems like this $20 deal at Amazon has been showing up every other day now.
Amazon will give you $10 off of a $100 order today if you purchase with MasterCard. Plus, get an additional $10 discount on a future order. The offer is only for today, December 20, 2011.
20% off at Amazon is a good dealAmazon promotional page
Today's savings code: 3TLRXE3N
Hat tip to the reader who emailed me news of this!