We partnered up with OsCommerce a while back. The project leader, Harald Ponce de Leon, deserves a lot of credit. It's a great product, free and opensource with an amazing amount of support resources available.
We host a few hundred osCommerce shops, and the clients stick with the OSC system year after year.
Jeff Standen, Chief of R&D, WebGroup Media LLC. - LinkedIn Cerb is a fast and flexible web-based platform for business collaboration and automation. http://www.cerbweb.com/