http://www.filleritem.com/ (and similar sites) are great for Amazon shopping.
Certain items at Amazon.com qualify for free shipping, but sometimes the purchase falls short of the minimum $25 needed to receive the free shipping. Enter the amount you need to see a list of products that qualify for free shipping
That particular filler item site also offers a firefox extension.
My mom wanted a book she had seen reviewed for her birthday. That and the previous book by the same author came to just shy of $25. When I called Mon for her birthday, she got a good laugh when I explained the carriage bolt that came with the 2 books. But as a Scot, she appreciated that a ~$1.25 carriage bolt saved me like $6 in shipping, so she liked the gift even better.
GREAT site if you shop Amazon & don't have Prime.