Here is the list of  Top 10 Mostly Downloaded Plugins of WordPress.This list may be very helpful for you if you’re new to WordPress or setting up a new WrodPress Blog.
1) All in One SEO Pack
Automatically optimizes your WordPress blog for Search Engines (Search Engine Optimization).
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2) Google XML Sitemaps
This plugin will generate a special XML sitemap which will help search engines to better index your blog.
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3) Contact Form 7
Just another contact form plugin. Simple but flexible.
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4) WP-PageNavi
Adds a more advanced paging navigation to your WordPress site.
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5) Akismet
Akismet checks your comments against the Akismet web service to see if they look like spam or not.
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6) BuddyPress
Social networking in a box. Build a social network for your company, school, sports team or niche community.
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7) Sociable
Automatically add links on your posts, pages and RSS feed to your favorite social bookmarking sites.
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Google Analytics for WordPress
The Google Analytics for WordPress plugin automatically tracks and segments all outbound links from within posts, comment author links.
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9) WP-SpamFree Anti-Spam
Powerful anti-spam plugin that eliminates blog comment spam. Finally, you can enjoy a spam-free WordPress blog! Includes contact form.
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10) Simple Tags
Simple Tags is THE perfect tool to manage perfectly your WP 2.8 and 2.9 tags (Tags suggestion, Mass Edit Terms (Tags and Category), Auto link tags.
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