I have been working lately with Magento (The state of Art e commerce platform). It is build upon the solid PHP Zend framework and uses MySQL as its database.
Magento comes with all the features which you can demand from your e-commerce solution. It is relatively new then other solutions but still it appears to be very stable and bug free (so far 
).
It probably provides more features than other commercial alternatives and yet the best part is it is free and open source.
Well thought and planned structure and features, ease of migration, flexible and simple templating system and many other features makes it a best choice for an e-commerce solution.
Kudos! to developers and magento community for such a great job!