There is a topic on the forum of joomlacommunity.eu about must have extensions. I'm always interested in finding and using extenions that make my life in Joomla easier so I decided to share these extensions, maybe you like them also.
Forms
Fields Attach
free
With Fields Attach you can add fields to an article or category. Examples of these fileds are : Input / Textarea / Select / Image / Gallery Image / File / Checkbox / Date / Radio Button / Youtube Video.
My Content & WorkFlow
paid
Your standard content in Joomla will be completed to real content management. You can edit, publish, unpublish and approve on the frontend of your website.
Content
Joomla Content Editor (JCE)
free
A highly configurable WYSIWYG editor for Joomla based on TinyMCE. For lots of Joomla users it's a must have extension.
Menu's
NoNumber Add To Menu
free paid
With Add to Menu you can make a menu link to a page from the administrator (page article or category).
Modules
NoNumber Advanced Module Manager
free paid
With Advanced Module Manager you will get lots of configuration options for your modules. You can control publishing modules on date, user group, language, template, OS or browser.
Security
Akeeba backup
free paid
Create backups or move your Joomla! website and easy to use. You can include or exclude custom maps or database tables.
Admin tools
free paid
With the free version you van fix permissions, alter prefixes and protect your administrator directory with a password. But the real power is in the paid version which contains a powerfull web firewall.
Alter Articles
paid
Extend the standard functionality of articles with maps, gallery, attachments and related articles.
SilverAdmin
paid
With SilverAdmin you can edit modules, menus en articles without login in the backend. It also ads a handy side menu in your website if your logged in.
Nonumber Cache Cleaner
free paid
When you edit an article you would like to see your changes on the frontpage without manual deleting cache files. With Cache Cleaner you get a quicklink to delete these cache files.
AutoArchive
free
You can remove, depublicise, archive or move content to a different category after a set date.