WooCommerce
WooCommerce is renowned open source e-commerce plugin for WordPress.
It is designed to enable WordPress sites to become e-commerce sites. It is particularly suited for small to large-sized online merchants.
The base software is open source, hence it is free. However, you may need to purchase additional plug-ins to achieve the functionality that you require, eg some payment provider connections.
It is proving very popular with clients, as it has many modern features.
