Check out these 20 WordPress Plugins and enhance your SEO, audience engagement and brand in 2011.

All the plugins listed here are tested with WordPress 3.2.1.  Hopefully, this article help make your site better and can act as a reference for fellow WordPress developers.

This Post has been updated with this one. Please refer to this post: Top 20 of the best WordPress plugins to use in 2011 – Tested with with WordPress 3.2.1 – Discover the wealth of WordPress

One of the reasons why people use WordPress is the seemingly unlimited numbers of open source plugins available.

This enables you to create a website and blog where visitors are engaged. Which is a key to success. It’s critical to create an experience that enables your web visitors to be easily entertained, engage and share your content with their network on the social networks as easily as possible.

Google Analytics for WordPress
Track your WordPress site easily and with lots of metadata: views per author & category, automatic tracking of outbound clicks and pageviews. This is great for gathering stats for Google Adsense and measuring your quality of content.

All in One SEO Pack
Out-of-the-box SEO for your WordPress blog.  Automatically optimizes your WordPress blog for Search Engines (Search Engine Optimization). This plugin offers almost all the SEO function you would like. Very recommended.

Contact Form 7
Contact Form 7 can manage multiple contact forms, plus you can customize the form and the mail contents flexibly with simple markup. The form supports Ajax-powered submitting, CAPTCHA, Akismet spam filtering and so on. Easy to integrate a contact form everywhere on your website.

Google XML Sitemaps
This plugin will generate a special XML sitemap which will help search engines like Google, Bing, Yahoo and Ask.com to better index your blog. With such a sitemap, it’s much easier for the crawlers to see the complete structure of your site and retrieve it more efficiently. The plugin supports all kinds of WordPress generated pages as well as custom URLs. Additionally it notifies all major search engines every time you create a post about the new content.

Revision Control
Revision Control is a plugin for WordPress 2.9+ which gives the user more control over the Revision functionality.

The plugin allows the user to set a site-global setting (Settings -> Revisions) for pages/posts to enable/disable/limit the number of revisions which are saved for the page/post. The user may change this setting on a per-page/post basis from the Revisions Meta box.

The plugin also allows the deletion of specific revisions via the Revisions post metabox.

Akismet
Akismet checks your comments against the Akismet web service to see if they look like spam or not and lets you review the spam it catches under your blog’s “Comments” admin screen.  This is a must if you want to avoid spam.

WPtouch
WPtouch automatically transforms your WordPress blog into an iPhone application-style theme, complete with ajax loading articles and effects, when viewed from iPhone, iPod touch, Android, Palm Pre, Samsung touch and BlackBerry Storm/Torch mobile devices.

The admin panel allows you to customize many aspects of its appearance, and deliver a fast, user-friendly and stylish version of your site to touch mobile visitors, without modifying a single bit of code (or affecting) your regular desktop theme.

WP-PageNavi
Replaces the basic ← Older posts | Newer posts → links with a more advanced paging navigation interface. Easy to install and lifts the design big time.

W3 Total Cache
The fastest and most complete WordPress performance optimization plugin. Trusted by many popular sites like: mashable.com, smashingmagazine.com, makeuseof.com, kiss925.com, pearsonified.com, lockergnome.com, tutsplus.com, johnchow.com, ilovetypography.com, webdesignerdepot.com, css-tricks.com, yoast.com and others — W3 Total Cache improves the user experience of your site by improving your server performance, caching every aspect of your site, reducing the download times and providing transparent content delivery network (CDN) integration.

Benefits:

• At least 10x improvement in overall site performance (Grade A in YSlow or significant Google Page Speed improvements)when fully configured
• Improve conversion rates and “site performance” which affect your site’s rank on Google.com
• “Instant” second page views (browser caching after first page view)
• Optimized progressive render (pages start rendering immediately)
• Reduced page load time: increased visitor time on site (visitors view more pages)
• Improved web server performance (sustain high traffic periods)
• Up to 80% bandwidth savings via minify and HTTP compression of HTML, CSS, JavaScript and feeds

WP-DBManager
Allows you to optimize database, repair database, backup database, restore database, delete backup database , drop/empty tables and run selected queries. Supports automatic scheduling of backing up, optimizing and repairing of database.

Digg Digg
This Integrate popular social buttons into WordPress easily and has easy access if you use the floating display.

• Display counts for popular social butons like Digg, LinkedIn, Google +1, Reddit, dDone, Twitter, TweetMeme, Topsy, Yahoo Buzz, facebook share, facebook like, StumbleUpon, Delicious, Sphinn, Google Buzz, Designbump, WebBlend, BlogEngage and Serpd.
• Facebook Like (Iframe or XFBXM), support thumbnail generation, multiple languages, show faces and send button.
• Rich button layout customisation.
• Flexible button display controls.
• Lazy loading to increase website performance.
• Left or right scrolling effect like Mashable.com.
• Support in excerpt mode.
• Support for email and print services.
• And many many ……

Fanpage Connect FREE
Fanpage Connect is the WordPress plugin that allows you to create an administer your Facebook fan pages directly from WordPress. Now you can power your Facebook Fan Page with your WordPress blog. In ONE click.Leverage the world’s most powerful blog engine and the social behemoth that is Facebook to maximize your business or brand’s exposure!Give your Fan Page the look and functionality that WordPress offers without all the friggin’ coding. No clunky “FBML”, no hand coding, and no development experience required. Just edit, publish and poof, your fan page is live!Keep your website looking like your website and your fan page looking like your fan page. Fanpage Connect works with any theme seamlessly and installs on your WordPress site in just a few clicks.

MySearchTermsPresenter (MySTP)
Boost your traffic and improve your adsense income and the search engine ranking without doing anything with MySearchTermPresenter.

This plugin will collect and present search terms and phrases that people have used to find your blog post.

MySearchTermPresenter will show a random list of used searchers to find a specific post on the bottom of the post.

Exclude Pages
This plugin adds a checkbox, “include this page in menus”, which is checked by default. If you uncheck it, the page will not appear in any listings of pages (which includes, and is usually limited to, your page navigation menus).

Pages which are children of excluded pages also do not show up in menu listings. (An alert in the editing screen, underneath the “include” checkbox allows you to track down which ancestor page is affecting child pages in this way.)

IGIT Related Post With Thumb UPDATE! DON’T USE THIS PLUGIN SINCE THIS INTRODUCES VULNERABLE PHP CODE!

• The IGIT Related Posts With Thumb After Posts Plugin Automatically inserts one widget after posts having related posts.
• Related Posts showing by title and content matching, If it not show related posts by title content matching it will search related posts by matching tags and title and if still it is not showing any related posts then it will show random posts.
• This plugin also empowers the Blog administrator to place manually related posts widget, Also having options to give related posts number,Display Thumb or not,Set Thumb Width and Height and Main thing it is giving three options to select related posts style – Horizontal, Vertical, Simple Style.
• By using this plugin on your blog you can attract your visitors to other related articles of your blog.
• This plugin is also SEO friendly.
• Ajax Based Admin Options.
• Exclude Categories from Related Posts.
• Note : This plugin is showing thumb images which are exists in posts and also exists on same server, Images from remote server are not showing in related posts to prevent bandwidth theft.

Smart 404
Optimize your SEO and Save your visitors from unhelpful 404 errors!

Instead of quickly giving up when a visitor reaches content that doesn’t exist, make an effort to guess what they were after in the first place. This plugin will perform a search of your posts, pages, tags and categories, using keywords from the requested URL. If there’s a match, redirect to that content instead of showing the error. If there’s more than one match, the 404 template can use some template tags to provide a list of suggestions to the visitor.

Smart Youtube
Handy plugin for integrating Youtube videos on your site. Smart Youtube is a WordPress Youtube Plugin that allows you to easily insert Youtube videos/playlists in your post, comments and in RSS feed.

The main purpose of the plugin is to correctly embed youtube videos into your blog post. The video will be shown in full in your RSS feed as well.

Smart youtube also supports playback of high quality videos, works on iPhone, produces xHTML valid code (unlike YouTube embed code), allows you to view videos in fullscreen, supports YouTube playlists (normal/HD) and the new outube IFRAME embed code.

The plugin is designed to be small and fast and not use any external resources. It has a number of customizable options.

TinyMCE Advanced
A recommended WYSIWYG editor for WordPress. Helps editing and writing posts. TinyMCE Advanced Enables advanced features and plugins in TinyMCE, the visual editor in WordPress. This plugin adds 16 plugins to TinyMCE: Advanced HR, Advanced Image, Advanced Link, Advanced List, Context Menu, Emotions (Smilies), Date and Time, IESpell, Layer, Nonbreaking, Print, Search and Replace, Style, Table, Visual Characters and XHTML Extras.

Subscribe2
Make it easier for you and your users to subscribe to your content. Subscribe2 provides a comprehensive subscription management and email notification system for WordPress blogs that sends email notifications to a list of subscribers when you publish new content to your blog.

Simple Facebook Connect
This plugin adds Facebook comments, publish new posts to Facebook, Login with Facebook, Facebook Connect and much much more. Simple Facebook Connect is a series of plugins that let you add any sort of Facebook Connect functionality you like to a WordPress blog. This lets you have an integrated site without a lot of coding, and still letting you customize it exactly the way you’d like.

First, you activate and set up the base plugin, which makes your site have basic Facebook Connect functionality. Then, each of the add-on plugins will let you add small pieces of specific Facebook-related functionality, one by one.