Here are the most downloaded Wordpress plugins. These most popular Wordpress plugins are downloaded a lot simply because they are very useful, easy to setup and use.
Easy and extremely productive spam-fighting plugin with many sophisticated solutions. Includes protection against trackback spam and privacy hints.
Form Maker is a user-friendly form builder plugin. This form builder lets you create contact forms and other questionnaires.
No setup required! You only need an SSL certificate, and this plugin will do the rest.
A simple yet powerful WordPress SMTP Plugin that uses smtp settings or phpmailer for sending emails. Re-configures wp_mail() function.
Use any image from your WordPress Media Library as a custom user avatar. Add your own Default Avatar.
WordPress Related Posts - the plugin for related posts with thumbnails. Caching included.
Extended Tagging for WordPress : Terms suggestion, Mass Edit Terms, Auto link Terms, Ajax Autocompletion, Click Terms, Advanced manage terms, etc.