We work extensively in various ecommerce frameworks, here we list some of the important resources that will help you find information quickly. This is ongoing research work and will change periodically. Please contribute new information, in case I have missed it.

1.0 Magento
http://www.magentocommerce.com/
2.Oscommerce
http://www.oscommerce.com/
3.0 ASP.NET DotNetNuke
http://www.dotnetnuke.com/

4.0 Apache Ofbiz- OFBIZ

5.0 Opencart- weblink