Here are some of the best Magento extensions that I’ve come across.

• Magento Live Chat – This free module will provide LiveChat support in Magento.
• Fontis WYSIWYG Editor – This extension gives you the option to enable a JavaScript WYSIWYG editor to specified admin pages. Currently available editors are: TinyMCE and FCKeditor.
• Lazzymonks Twitter – Displays Twitter updates in the menu and allows updates from within the admin panel.
• Events Calendar – With this extension, you can display an events calendar on your website. Events are stored in the database. You can also display the upcoming list of events quickly by calling a block in your template.
• Blog – Full featured blog extension for Magento.
• Raffle – This module gives you basic functionality to run your own raffles.
• Customer Groups Configurable Catalog – This extension enables you to hide categories and products from customers depending on the customer group.
• Exploded Menu – Replaces the standard single column drop down with a multi-column dropdown featuring 2nd and 3rd level menu items.
• Velite Magento Superstage – Functionality, intuitive interaction and product presentation with really high detailed images are the main features.
• Magento EasyLightbox – This small extension will help to install Lightbox widget. Installation and configuration will take approximately 5 minutes. No files are replaced and no codding experience needed to install!
• Magento Exploded Menu – Replaces the standard Magento menu with a multi-column drop down menu system.