Based on the osCommerce engine, Autoload incorporates the best contributions available: Quickbooks import, real time shipping rates though UPS and USPS (among others), PayPal, Google Checkout, almost any payment processor. Auctionblox eBay management, Easypopulate to easily import your products, Dynamic Header Tags and search engine optimizing, multiple images, produce .pdf datasheets, products with multiple images and attributes, and more. All the functions most people would want. Many security enhancements are built in and the script is PHP5/mySQL5 ok.
Autoload is a standard shopping cart solution and is very portable.
Does everything I need it to.