I've been an Amazon Prime member since Amazon first offered it. I buy almost all my Christmas and birthday presents from them, so the service pays for itself.
I can also share it with up to four other people, so my sibs are Amazon Prime members, too.
Not everybody is. My pal, Spider, asked me the other day what she could buy at Amazon that would bring her total high enough to get free shipping. Here's the tool for her: the Amazon Filler Item Finder.
This is cool technology and interesting design: a micro-service that does one thing, well. The web site is, itself, cool because it's so minimalist.