If you particularly want a CMS system with an ecommerce solution included, I would suggest virtuemart.

VirtueMart: Your free e-commerce solution. - Welcome....

It integrates with Joomla and is free. You can download a script with virtuemart already integrated into Joomla which is easy to install.

I have built 3 sites with osCommerce , which would do want you want as well, but I found virtuemart a lot easier to work with, especially with skinning the site, and getting the basic parameters up and running.

Of course, all scripts of this size have a steep learning curve to jump over.