For a long time I refused to sign up for Amazon Prime, and I'd order things that cost $19 or $23, and I'd hunt around for something that would bring in that additional $6 or $3 to meet the minimum price for free Super Saver Shipping (USD $25). I got tired of hunting around for that, so I built http://finishmyorder.com/.

I get like $6/mo in affiliate fees, but I don't really advertise it so I'm lucky I get even that.