Sociable Skyscraper is the ultimate advanced and feature-packed plugin for setting up a rating system on your WordPress blog. This plugin allows you to set up different rating systems for posts, pages and comments with a great degree of customization.
Just another contact form plugin. Simple but flexible.
Make Your Site Social by integrating Gigyas social optimization service into your WordPress site.
IntenseDebate is a feature-rich comment system for WordPress, Blogger, Tumblr and many other blogging/CMS platforms.
Adds a more advanced paging navigation interface.
Track how’s your blog doing across the leading social networking websites and services.
Your all in one share buttons plugin. Add a floating bar with share buttons to your blog. Just like Mashable.
If you have a Facebook profile or page or a Twitter account, this plugin is what you need to connect them with your blog!
Display a Facebook Fan Box on your blog. Put the Facebook Fan Box in your sidebar using the widget mode or call the function inside your template.