There are way too many extensions in the wordpress directory to truly make a Top list since so many of them are excellent. We do, however, have some favourite we thought we’d share in order to help them get some more exposure. Here they are in no particular order or ranking
Here, I will list you 28 most useful WordPress plug-ins. These plug-ins can easily extend your WP functionality and productivity. Giving your blog more professional look and some very useful and good features and options completely for free.
Automatic Search Engine Optimization (SEO) out of the box for your wordpress blog.
WP Super Cache is a static caching plugin for WordPress. It generates html files that are served directly by Apache without processing comparatively heavy PHP scripts. By using this plugin you will speed up yourWordPress blog significantly.
Easy AdSenser provides a very easy way to insert Google AdSense code into your existing blog posts. It gives you a widget to display ads in your sidebar, and another to show a Google Search box. Easy AdSenser is perhaps the first plugin that gives you a complete solution for managing everything AdSense-related.
This plugin will create a Google sitemaps compliant XML-Sitemap of your WordPress blog. It supports all of the WordPress generated pages as well as custom ones. Everytime you edit or create a post, your sitemap is updated and all major search engines that support the sitemap protocol, like ASK.com, Google, MSN Search and YAHOO, are notified about the update.
This plugin allows you to automatically post your new posts on the twitter website.
cforms is a highly customizable, flexible and powerful form builder plugin, covering a variety of use cases and features from attachments to multi form management, you can even have multiple forms on the same page.
Pass a bit of luv onto your commenters by providing a titled link to their last blog post. This plugin attempts to parse the feed of the comment author by visiting their site and looking for their feed while they type their comment and appends it once they submit.
Helps readers subscribe to your blog using any feed reader, such as Google Reader, My Yahoo!, Netvibes, Windows Live, and all the rest. The button comes with Add to Any’s customizable Smart Menu, which places the services visitors use at the top of the menu, based on each visitor’s browsing history.
This plugin shows excerpts of the latest comments and/or trackbacks in your sidebar. You have comprehensive control about their appearance. This ranges from the number of comments, the length of the excerpts up to the html layout. You can let the plugin order the comments by the corresponding post, or simply order them by date.
Adds an AJAX rating system for your WordPress blog’s post/page
WP reCAPTCHA is an anti-spam method originating from Carnegie Mellon University which uses CAPTCHAs in a genius way. Instead of randomly generating useless characters which users grow tired of continuosly typing in, risking the possibility that spammers will eventually write sophisticated spam bots which use OCR libraries to read the characters, reCAPTCHA uses a different approach.
Yet Another Related Posts Plugin gives you a list of posts and/or pages related to the current entry, introducing the reader to other relevant content on your site.
WP-GravatarWordpress Popular Posts is a sidebar widget to show the most popular posts in your blog. Many options has been included in it so you can customize it to your liking.
15. Do Follow
The dofollow plugin for WordPress lets you remove the evil nofollow attribute from your comments. Because nofollow will not work.
16. Add-Meta-Tags WordPress Plugin
This plugin adds XHTML META tags to your WordPress blog. The addition of the META tags is fully automatic , but it also includes all those features a SEO-concerned publisher would need in order to have total control over those meta tags.
17. Tweet This
A plugin that adds a Twitter link to every post and page, so your readers can share your blog entries on their Twitter accounts with ease. Shortens URLs in advance.
18. Global Translator
Global Translator is a free and open source WordPress Plugin which is able to automatically translate your blog in 41 different languages.
19. Audio Player WordPress plugin -
One one simple audioplayer plugin for WordPress
20. Related Posts
One way to increase your blog page view is by adding links to posts which are related to the one they are currently reading. You can do this with Related Posts plugin which automatically returns a list of related entries based on active/passive keyword matches.
21. WordPress DatabaseBackup
Backing up your wordpress database should be done frequently especially when you are adding content actively. WordPress DatabaseBackup offers a one click database backup to help you backup your data easily. You may download the backup file, or have it emailed to the address of your choice. It’s included in WordPress 2.0. by default but you’ll have to enable it.
22. Optimal Title
You’ve done everything to make your blog pretty and functional, you’ve added useful content for your visitors, so what’s next? You might want to optimize your blog for the search engines and one way to do this by installing Optimal Title which will turn your blog title into something more meaningful for the search engine.
The AddThis Social Bookmarking Widget allows your users to bookmark your site easily with over 45 popular services, and to share it with friends via email. Our button is small, unobtrusive, quick to load and recognized all over the web.
24. Lightbox 2
It is used to overlie images on the current page
25. Referrer Detector
Traffic to your blog can come from a variety of sources. Referrer Detector is a handy WordPress plugin to display a greet box for visitors that come from various source (like Digg, StumbleUpon, Technorati, Google Search etc.) This plugin makes sure that they are greeted with a personalized welcome message and a nice reminder that positive votes are always appreciated. For an example, If you’re a Digger, and you’re coming from Digg.com, you’ll be welcomed with this box instead:
Another community building plug-in. It let’s you place the small pictures (avatars) of your readers next to their comments on your blog. Makes the comment area and the discussion much more personal and lively. In order for the avatars to appear, reader has to register it with Gravatars service.
You probably noticed small icons from various social bookmarking sites (like Digg, del.icio.us, reddit, etc;) under the posts on many blogs. Well, lot’s of them are done by this plugin. So if you want to help your users spread the word about your best posts, you may want to install this plugin.
28. WP-Page Navi
is a plugin to improve page navigation on your blog. Instead of having to go through blog pages one by one, it adds better navigation functionality that can look like this: Pages (17):  2 3 4 » … Last »