I have done some extensive research and testing of many extensions for Joomla CMS. I have found many very bad extensions and some very good ones. Below is the list of extensions I recommend.

Plugins

AllVideos by JoomlaWorks

Core Design Magic Tabs plugin by Core Design

Core Design Scriptegrator plugin by Core Design

Modules

AdSense Module (ClickSafe - Special Edition) by Joomlaspan

Core Design Login Module by Core Design

googleSearch module by kksou.com

jWeather by p0l0

Componets

RSGallery2 by RSGallery2.net Team

JCE by Joomla Content Editor

googleSearch component by kksou.com

ChronoForms by ChronoEngine