I've been using Joomla open source CMS over three years now. In my web development journey i have used hundreds of commercial and non-commercial extensions for various volunteer and commercial projects. As you know Joomla is serving more than eight thousands extensions to the community. I have found some of the extensions very useful, like i can't live without them. You may not like all components i've listed here and you may also think that there are many other useful stuffs. But i can't enlist all of them in this my top ten favorite list. These list are mainly Joomla components, there are many other modules and plugins which are very useful too. I will try to list them separately in my future posts.

I hope you are not getting confusion about what these joomla extensions are. I want to make it simple, Joomla extensions are , templates, modules, components or plugins that extends your Joomla! installation. They come included in Joomla core or can be provided from 3rd party developers. If you would like to know more about joomla extensions please visit this link Joomla extensions directory.

1. Virtuemart [Shopping Cart]

VirtueMart is a PHP-based Shopping Cart Application for selling goods over the internet. It's a Component (= plugin) for a Content Management System called Joomla! (and Mambo) and can't be used without Joomla!. It installs fairly easy using the automatic Component and Module Installer. It's intended for use in small / mid-sized Online Businesses / Online-Shops. So every user who wants to build up a Online Store can use this Component for selling something to Customers.

VirtueMart offers a lof of Features, some of the standard Features are listed here. Please note that you can extend the Functionality of Joomla! and VirtueMart using Plugins, Components, Templates and Modules to make them do what you need!

2. Phoca Gallery [Image Gallery]

Phoca Gallery is a Joomla! gallery - image gallery for Joomla! CMS. It includes component, modules and plugins and allows users to display images or Youtube videos in many different styles.

Phoca Gallery creates 3 types of thumbnails to show the pictures. Those thumbnails are created with the help of the GD library (which you need to be enabled on your server). The smallest thumbnail is used when you display a list of categories. The medium thumbnail is used when you display the images in a category and the large thumbnail pops up when you click a medium thumbnail. Then you can also start a slideshow to view the images which belong to a category. The original image is used to create thumbnails from and a link can be displayed that visitors can display/download the original image. The advantage of using also large thumbnails is that you can add watermarks to your thumbnails, all large images are the same size (maximum). You can define the sizes yourself. There are a lot more features. See the feature list.

3. K2 [CCK]

K2 provides an out-of-the box integrated solution featuring rich content forms for items (think of Joomla! articles with additional fields for article images, videos, image galleries and attachments), nested-level categories, tags, comments, a system to extend the item base form with additional fields (similar to CCK for those acquainted with Drupal), a powerful plugin API to extend item, category and user forms, ACL, frontend editing, sub-templates and a lot more!
Using K2, you can transform your Joomla! website to a news/magazine site with author blogs, product catalogs, work portfolio, knowledge base, download/document manager, directory listing, event listing and more, all this bundled under one package!
Give K2 a try and you'll instantly love it! It's easy to use and fun to develop websites with! If you need any help or want to contribute to the project, join us at the K2 community.

4. Community Builder [Community Profile]

CB has many CB plugins from CB Team and from third parties, including Profile Gallery, Profile Blog, Profile Guestbook, Profile Wall, Facebook Connect, Twitter Connect, Paid Subscriptions Membership management, Donations management, Shop, Captcha and many more. Over 200 extensions for CB are listed here (see link below) and on the Joomlapolis directory.

CB has many CB plugins from CB Team and from third parties, including Profile Gallery, Profile Blog, Profile Guestbook, Profile Wall, Facebook Connect, Twitter Connect, Paid Subscriptions Membership management, Donations management, Shop, Captcha and many more. Over 200 extensions for CB are listed here (see link below) and on the Joomlapolis directory.

CB allows multi-criteria user searches, full field controls of core fields, ajax email and username checkers, image and integer fields, custom validations and many more features. CB is open-source and free.

5. JCal Pro [Even Manager]

JCal Pro is a W3C-validated, multi-language events calendar component with a gorgeous, CSS-based front-end display. Feature highlights include, native Joomla! permissioning for event creation/management and event viewing, multiple calendars including private or public calendars, WYSIWYG event descriptions, administrative theme installation and management, back-end event management, re-captcha support, an integrated search plugin, feature-rich mini-calendar and latest events modules, the all new FLEX module, a convenient content editor plugin, RSS feeds, SEF URL support, robust print-views, JomSocial plugins and Community Builder plugins.

6. JCE Editor [WYSIWYG editor]

Add a set of tools to your Joomla!® environment that give you the power to create the kind of content you want, without limitations, and without needing to know or learn HTML, XHTML, CSS. It has Office-like functions and familiar buttons make formatting simple, Upload, rename, delete, cut/copy/paste images and insert them into your articles using an intuitive and familiar interface, Create Links to other Sections, Categories, Articles, Weblinks and Contacts¹ in your site using a unique and practical Link Browser, Take control of your code with syntax highlighting in the Advanced Code editor and advanced style and element attribute editing and Integrated Spellchecking using Google™ Spellchecker (or PSpell and ASpell).

7. Joomfish [Language Manager]

JoomFish is the solution for your multilingual website if control over the translations matters for you. The core extension is free of charge and allows the translation of any content within your Joomla system. With an easy extension it is also possible to translate any 3rd party extension available for your favored CMS.

JoomFish 2.1 is the full featured release including several addons such as a simple Router for your SEO URL's and automatic search within the core extensions of Joomla. It comes with an integrated one step installer that allows you to get started very simple.
Free documentation including video tutorials, first step documentations and additional material is available on our website. The site also includes an open forum for community support and additional resources.

8. DOCman [Document Manager]

DOCman is a document management solution for Joomla. DOCman makes offering downloadable documents on your Joomla site a breeze.

Manage documents across multiple categories and subcategories, give users permission to upload, download or edit documents. Store documents either locally or remotely and prevent direct linking using our build-in anti-leech system. All from within an intuitive and simple to use administration interface.

9. Kunena [Discussion Board]

Kunena - The leading Joomla Forum Component. Downloaded more than 1,400,000 times in the 2 years since its start. The only forum/discussion solution for Joomla that is community driven. No hidden fees, no surprises - true open source. See our public forums, SVN and file repositories, our public documentation wiki.

The Kunena Team has now released Kunena 1.6.5 as a native Joomla extension for J! 1.5.23 and J! 1.6.6 AND J! 1.7.0. This is a maintenance release for Kunena 1.6 and all users are recommended to upgrade to Kunena 1.6.5 (backup and testing are strongly recommended!).

10. xmap [Sitemap Generator]

Xmap is a new component based on the popular Joomap component. Xmap allows you to create a map of your site using the structure of your menus. This component adds new powerfull options to Joomap and fixes several bugs reported by many users of Joomap.

I hope you will find these useful to develop your Joomla sites. I would love to hear your favorite extensions in comment box.