Joomla! really is an install and plug and play (and plug some more and play some more) approach to website development and management. There is a base functionality that comes with Joomla! and when you decide that you need "a shop" or "a commenting system" or "more complete statistics" or "the ability to work/visit in several languages" or, or, or... odds are that someone somewhere has developed an extension for this.
After having tested many plug-ins, components and modules, here is a suite of site extensions that I consider to be "the best of the best". My selection criteria includes ease of use, solidity of code, clean and non-conflictual delivery of functionality, control over the aesthetics and good community/developer support. Many of these are freeware. Some are donateware. Some are commercial licenses. They are all excellent.
akoComment TSE
This is definitely the best commenting system I've found for Joomla!.
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AllVideos Plugin
To embed videos/audio on your site, this plug-in makes things easy.
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astatsPRO
If you are looking for a friendly and flexible way to see and display your site statistics, astasPRO is probably what you're looking for.
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Community Builder
Community Builder is an excellent extension for strong community oriented sites.
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DOCMan
A document up/download management system for the front-end of Joomla!.
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Facile Forms
FacileForms is a great way to generate and manage forms and form data.
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Fireboard Forum
If you are looking for a forum, this is the one I suggest.
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iJoomla Magazine
If you wish to publish issues of news, this commercially licensed component could be what you're looking for.
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iJoomla SideBars
All of the sidebars on this site are generated using this commercially licensed plug-in.
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Joom!Fish
If you wish your site to be available in more than one language, this is the plug-in you need.
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JoomlaXplorer
To browse, manage and edit files from within Joomla!, this is the component you'll want.
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Letterman
This is the best rated newsletter component for Joomla!.
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RokGuest / RokMember
This plug-in lets you display different content within a single article to guests and/or members.
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RokSlideshow
A simple and effective slideshow. (Uses Mootols.)
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Simple Image Gallery
A simple way to add galleries inside your content. (Freely distributed version.)
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Simple Image Gallery PRO
A simple way to add galleries inside your content. (Commerically licensed version.)
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Simple Image Rotator
Another simple slideshow plug-in.
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Slimbox
A plug-in that displays thumbnails in an overlay.
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SSL certificate
For a secure site...
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VirtueMart
If you are looking for a shop functionality, look no further.
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zOOm Media Gallery
A great gallery component.
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