Virtuemart is the the most commonly used shopping cart component for Joomla!

Virtuemart allows you to showcase a large range of products, arranged in categories and sub-categories for view and sale on your website.  Virtuemart is the most versatile shopping cart available for use with Joomla sites and allows you to define product attributes, offer discounts, add multiple pictures for each product and put items on sale for a defined period.  Virtuemart is also compatible with most payment gateways.