We build various eCommerce solutions using a range of open source software. For many users Joomla! with Virtuemart is a good solution. However, for flexibility and enterprise level features we prefer to use Magento.
Magento eCommerce Platforms provide the scalability, flexibility and features for business growth. Magento provides feature-rich eCommerce platforms that offer users complete flexibility and control over the presentation, content, and functionality of their online channel.
eBay have recently agreed to aquire Magento so its future is ensured.
An added bonus is we have recently found a fantastic addon for Magento that allows you to upload products really fast. One weakness of Magento is loading products. Now with Magmi (Magento Mass Importer) we are able to load thousands of products in minutes.
Take a look at a Magento store we've recently built for a busy record producer here.