On his blog today, Vinu Thomas spotlights one of the major up and comers in the PHP-based eCommerce software package offerings - Magento.
Magento is an ecommerce platform on PHP which is quite feature rich. This platform is based on the Zend Platform. You can take a look at a Magento store and the admin demo over at their demo section.
He mentions some of the features it has including analytics, catalog management, order management, payment integration with Paypal/Google Checkout/Authorize.net and some SEO optimizations.
You can find out more over on the project's website and download your own copy or peruse the forums to get to know the community around this popular app.