WordPress is becoming the most powerful tool for building the websites. Because wordpress has greatest SEO support.
If you have wordpress website then you need to add following wordpress plugin which are free. Following plugin will make your blog more social.
1. Akismet http://akismet.com/
Akismet checks your comments against the Akismet web service to see if they look like spam or not. You need a WordPress.com API key to use it. You can review the spam it catches under “Comments.” To show off your Akismet stats just put <?php akismet_counter(); ?> in your template.
2. Contact Form 7 http://contactform7.com/
Just another contact form plugin. Simple but flexible.
3. Digg This http://www.aviransplace.com/index.php/digg-this-wordpress-plugin/
Adds Digg story link on detection of digg referer
4. FaceBook Share (New) http://wordpress.org/extend/plugins/facebook-share-new/
Adds a button which allows you to share post and also shows the number of times the post or page has been shared through out the Facebook just like tweetmeme button does for twitter.
5. Google XML Sitemaps with qTranslate Support
6. Limit Posts http://labitacora.net/comunBlog/limit-post.phps
Limits the displayed text length on the index page entries and generates a link to a page to read the full content if its bigger than the selected maximum length.
7. Most Commented http://mtdewvirus.com/code/wordpress-plugins/
Retrieves a list of the posts with the most comments. Modified for Last X days — by DJ Chuang www.djchuang.com
8. Popularity Contest http://alexking.org/projects/wordpress
This will enable ranking of your posts by popularity; using the behavior of your visitors to determine each post’s popularity. You set a value (or use the default value) for every post view, comment, etc. and the popularity of your posts is calculated based on those values. Once you have activated the plugin, you can configure the Popularity Values and View Reports. You can also use the included Template Tags to display post popularity and lists of popular posts on your blog.
9. Related Posts http://www.rene-ade.de/inhalte/wordpress-plugin-relatedposts.html
This wordpress plugin provides tagcloud that shows the related posts of a post, and can replace a keyword within a post to a list of related posts.
10. SEO Ultimate http://www.seodesignsolutions.com/wordpress-seo/
This all-in-one SEO plugin gives you control over titles, noindex, meta data, slugs, canonical tags, “more” links, 404 error tracking, and more.
11. TweetMeme Retweet Button http://tweetmeme.com/about/plugins
Adds a button which easily lets you retweet your blog posts.
12. Webmaster Tools Verification http://www.jamespegram.com/webmaster-tools-verification
All three of the major search engines have some type of website service. This plugin allows you to easily add the ability to verify your site with Google Webmaster Tools, Yahoo Site Explorer and Bing Webmaster Center. Works with both WordPress and WordPress MU
13. WordPress.com Stats http://wordpress.org/extend/plugins/stats/
Tracks views, post/page views, referrers, and clicks. Requires a WordPress.com API key.
14. WP-MostCommentedPosts http://ja.rafi.pl/2006/05/01/wp-most-commented-posts/
WP-MostCommentedPosts plugin by Rafal “RAFi” Krawczyk based on WP-STATS Statistics Plugin for WordPress
15. WP-PageNavi http://lesterchan.net/portfolio/programming/php/
Adds a more advanced paging navigation to your WordPress blog.
16. WPtouch iPhone Theme http://bravenewcode.com/wptouch
A plugin which formats your site with a mobile theme for the Apple iPhone / iPod touch, Google Android and other touch-based smartphones.