WooCommerce seems to be very popular these days. I did a site with WC and found their addons pretty much run the gamut of what most storefronts need including varieties of payment processors, shipping estimates through UPS and USPS. Each addon comes at a price but they're priced to sell and allow you to cobble together only the blocks your store calls for.
Keep on Coding! Mark Cicchetti - There are 10 kinds of people... those who understand binary and those who don't.