When it comes to create an e-commerce web site without any custom development, osCommerce is the usual choice. Of course, there are alternatives, but most are not as powerful as osCommerce.
But things have changed and if you need to create an e-commerce web site, I’d strongly advise you have a look at Magento Commerce. See the Demo shop to have an idea of what it looks like.
Of course, Magento is open-source software and you get a full-featured, professional-looking web site after a few clicks.