I thought it would be useful to have a link to All the extentions we use on our Joomla 1.5.x sites....
- please put (cost) if you must pay for the extention...
Site Wide & Site Tools
Backup and Restore of Joomla site
http://www.akeebabackup.com/ Joomla Backup (formerly JoomlaPack)
Admin Tools - One click update of your core Joomla system
Sitemap (with google feature)
Feedback & Forms
Learning Management System
Flash quizzes and questionnaires
Live communication tool