One of the most coolest advantages of Joomla is the extensible ability; you know, with 9000+ extensions on Joomla Extensions Directory (JED).
However, if you are new to Joomla & get confused with what extensions are necessary for your website, take a look at the inforgraphic about 9 must-have Joomla 2.5 extensions below. Thanks to them, you can use Joomla more easily and more securely. You can also do SEO on your website better.
All feedbacks are appreciated. You can give them in the comments below.