The most dominant ecommerce plugin for WordPress is WooCommerce.

WooCommerce.com produce its own theme designed especially to support the WooCommerce plugin called Storefront.

[see Storefront on WordPress.org] / [see Storefront on WooCommerce.com]

There are thousands of other themes that are built with WooCommerce support.

[see FREE WooCommerce-supported themes on WordPress.org] / [see PAID WooCommerce-supported themes on ThemeForest]