I like www.sparkplugs.com
I order a bunch of plugs, for all of my vehicles, each year, all at once to save on shipping.
I love fine-wire iridium plugs, run them in all my vehicles. Hardluk is right, your vehicle may not need them, and you may get no advantage (and be out a few bucks). Some of my more tempermental vehicles (prone to fouling, etc.) DO need them, and they are MUCH better than normal plugs there. So I run them in each vehicle that will take them (correction, not my cars, bikes only).