Here is a list of some commonly used Joomla extensions:

• http://www.chr00t.com/2007/02/joomla-popular-plugins/
• http://www.s-go.net/index.php/s-go-blog/215-top-10-joomla-plug-ins-and-add-ons
• http://www.techprone.com/top-10-ultimate-joomla-extensions/
• http://www.joomlashack.com/joomla-extensions/381-ultimate-top-ten-joomla-extensions-revealed
• http://sandeephegde.me/2009/09/04/top-10-free-joomla-extentions/
• http://www.makeuseof.com/tag/10-free-joomla-extensions-live/
• http://www.yjoomla.com/top-joomla-extensions-those-are-most-used.html