Amazon.com currently has a 4-for-3 Promotion on many products in Home & Garden.  Essentially, when you get four eligible items, the lowest-priced item out of the four becomes free during checkout through automatic discount.  Details are described here.  Note that there is a similar promotion on books that can be combined with these Home & Garden products.  At the time of this post, there are over 58,000 Home & Garden products that are eligible for this promotion.
Originally posted earlier, this is just a friendly reminder.