My husband recently discovered this trick for online shopping. Here are some links to use to look up the merchant that you are using or you can look up a particular product to find a merchant. Then these websites will give you various promotion codes to use when you check-out to get different deals such as free shipping, or 25% off, or whatever it happens to be. I've been doing this ever since he told me about it and I've found some great deals. It works best with larger merchants like Wal-Mart, Target, or JoAnn. You can also do a search for "promotional codes" or "printable coupons" and get deals that way.
http://www.retailmenot.com/
http://www.promotioncodes.com/
http://www.promotioncode.org/