JCE is another popular extension of Joomla. JCE is a free content editor that provides the web designers with a set of WYSIWYG editing tools. The JCE is free, extendable and can also be customized according to the requirement of the designer. It makes writing articles for Joomla web design and related things a tad bit easier.
Xmap is based on the hugely popular Joomap extension. It allows you to create a map of the site you are designing based on the structure of your menus. It also fixes several bugs that had been reported by many Joomap users in the past.
JoomlaXplorer is the File and FTP manager. It allows you to edit, copy, delete, rename and archive files directly on the server. Using the JoomlaXplorer is easy and that is probably the reason why it is so popular with web developer these days.
RokSlideShow is a wonderful plug-in with magnificent slideshow capability. You can use this extension to put various slideshows on your webpage. Right now, this software is a little resource intensive. But its efficiency makes it one of the most popular Joomla extensions today.
If it is a forum you are designing then it is important that you utilize ccBoard . It works incredibly well with Joomla. Although, in many ways it is similar to phpBB3, the ccBoard has certainly created a niche out for itself in the hearts and minds of the web developers. It is fast, attractive and comes with loads of features. Easily one of the best (probably the best) forum platforms available for Joomla.
VirtueMart is a fully featured open source e-commerce solution that is used together with Joomla. It is used in conjunction with Joomla since they are both written in PHP and can only be used in PHP environments. Through the VirtueMart you can set up your own shop online and start selling your goods and services.
Jumi is a built-in custom code extension used for Joomla. Its flexible nature allows you to include HTML, CSS, PHP as well as plain text files very quickly into you Joomla.