eCommerce themes are designed specifically for websites which sell products online.
While there's a limited amount of free themes for this purpose available, some people are willing to pay for a premium theme which provides premium technical support and upgrades.
Here's a list of the latest premium eCommerce themes for WordPress.
What you don't find in this list i'm sure you'll find in the Ultimate List of Premium Themes for WordPress.
Check out the huge range of eCommerce extensions for WooCommerce.
There's also a range of non official extensions at Code Canyon at a far cheaper price and a range of free and premium eCommerce themes.
One of the best eCommerce plugins to use with your theme is Woo Commerce.
Whats your favorite theme and plugin combination?
What do you plan on selling or what are you selling online now?