If you want to focus on the business and not so much the site work, I'd recommend looking in to BigCommerce.com, Shopify.com, and Wordpress/WooCommerce.com. I've used them all, while 3DCart I have only demo'd and was not overly impressed. As headz points out the squarespace offering, I'll definitely be interested in seeing how well it compliments their traditional web site offering. Shopify is really quite easy to use and get up and running, and there are a ton of great themes available. BigCommerce is definitely more robust and feature-intensive, which may not be something that you need. It requires more hand holding. If you have done any Wordpress work, Woootheme's WooCommerce might be a good option. Any of these would be great for getting your feet wet and not get you so bogged down in building something out that may or may not be the best use of your time. Sometimes it's better to let ready-to-go ecommerce platforms handle the heavy lifting while you prove out your concept.