No brainer. Open source CMS. They are extensible and rich plugin markets. Current leaders are wordpress, joomla, Dotnet nuke, Umbraco and drupal, but there are many others. Word press has around 13,000 plugins for everything from ecommerce to social networks but all most all them have that.
One consideration is that dotnetnuke and umbraco target the enterprise so can be somewhat heavy weight. More modern CMSs are lighter weight. Orchard.net, for example is a .net mvc3 application whose core is very small and even the basic features are design as external modules.
One consideration is that dotnetnuke and umbraco target the enterprise so can be somewhat heavy weight. More modern CMSs are lighter weight. Orchard.net, for example is a .net mvc3 application whose core is very small and even the basic features are design as external modules.