WordPress is the world famous open source based blogging software with a focus on aesthetics, web standards, and usability. WordPress is both free and priceless at the same time. Plugins can extend WordPress to do almost anything. Here is the list of Top 10 most commonly used (downloaded) wordpress plugins.
All in One SEO Pack – Automatically optimizes your WordPress blog for Search Engines (Search Engine Optimization).
Google XML Sitemaps – This plugin will create a Google sitemaps compliant XML-Sitemap of your WordPress blog.
Akismet – WordPress Akismet checks your comments against the Akismet web service to see if they look like spam or not.
Contact Form 7 – WordPress contact form plugin. Simple but flexible.
Google Analytics for WordPress – The Google Analytics for WordPress plugin automatically tracks and segments all outbound links from within posts, comment author links, links within comments, blogroll links and downloads.
Add to Any: Share/Bookmark/Email Button – Help readers share, save, bookmark, and email your posts and pages using any service, such as Facebook, Twitter, Digg, Delicious and over 100 more.
NextGEN Gallery – NextGEN Gallery is a full integrated Image Gallery plugin for WordPress with a Flash slideshow option.
GD Star Rating – GD Star Rating plugin allows you to set up advanced rating and review system for posts, pages and comments in your blog using single, multi and thumbs
WP Super Cache – A very fast caching engine for WordPress that produces static html files.