WordPress — the open-source content management system that runs this site and millions of others around the world — is almost infinitely extensible, which was the intention of the development team from the beginning.

One of the core philosophies of WordPress is to keep the core code as light and fast as possible but to provide a rich framework for the huge community to expand what WordPress can do, limited only by their imagination. Plugins can extend WordPress to do almost anything you can imagine…

But there are more than 3,000 WordPress plugins to choose from so if you’re new to this, where do you start? After building several dozen WordPress sites, from simple one-page blogs to complex web-zines, we’re finding these 10 plugins among the most useful:

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.

All-in-one SEO Pack Automatically optimizes your page titles for search engines (SEO). Generates META tags automatically andavoids the typical duplicate content found on WordPress blogs.You can override any title and set any META description and any META keywords you want, and can fine-tune everything to your hearts content.
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.
Google XML Sitemaps 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.
Lock-out This plugin will allow you to put your website into Lock Out mode to prevent access while you preform upgrades or maintenance. Includes the ability to upload a pre-made html file for use as a placeholder page while in lock out mode or build your own online. The login page is still accessible and will allow only the user role you set to view the site normally while in lock out mode.
Reveal ID’s With WordPress 2.5 and later the IDs on all admin pages have been removed, probably due to the fact that the common user don’t need them. However, for advanced WordPress Users/ developers those IDs are quite useful. This plugin makes them easy to find.
Stat Press We love Google Analytics but their reports lag 24 hours and sometimes you want to see what’s happening right now. For that you need Stat Press. This real-time plugin is dedicated to the management of statistics about. It collects information about visitors, spiders, search keywords, feeds, browsers etc. and reports them as they happen. Think your site is slow because traffic is spiking? Here’s how to find out.
WP Polls What do your visitors think? Ask them with WP-Polls which is extremely customizable via templates and css styles and there are tons of options for you to choose to ensure that WP-Polls runs the way you wanted. It now supports multiple selection of answers.
WP Super Cache This plugin generates static html files from your dynamic WordPress blog. After a html file is generated your webserver will serve that file instead of processing the comparatively heavier and more expensive WordPress PHP scripts.
WP Automatic Upgrade WordPress Automatic Upgrade allows a user to automatically upgrade their installation to the latest one provided by wordpress.org in 5 steps that include complete site and database backups, deactivation and re-activation of plug-ins.

Don’t see what you need? Search the Plugins Directory or learn to write one yourself.