Magento
Since I last looked (around 9 months ago, I think) the Magento web store project seems to have shaped up nicely. It is certainly prettier than OSCommerce, but more importantly they have kept the code and the presentation separate using – of course – CSS.
It is written in PHP, and has a growing collection of add-ins, so I’ll be seriously evaluating it as an alternative to OSC for the Oriental Food Shop.