Thursdays are when ARe usually holds publisher-centric flash sales. They don't do them every week, but it's a good idea to keep an eye out for them.
Second, BN.com has a 15% off coupon good until 3/29. Use 89RQJS2W2U138 at checkout. It's a one-time use code per customer and there are restrictions (no discounts on NOOK readers and select products.