joomla with virtuemart has proven managable for me, i don't like the not terribly seo friendly urls it makes, and the meta description requires a similar trick to my wordpress one (detailed in a wordpress thread on here somewhere), but once you've found the right file, edited it to create a dynamically generated custom meta description tag, and installed csvi (the .csv product management tool that lets you mass update your product inventory) you end up with a faily good site, that is easy enough to manage that you can just hand the keys over to a not quite so savvy client and not be terribly worried about them breaking it