WordPress is arguably one of the most powerful and easy to use content management systems out on the free market today, which gives host to a huge array of downloadable plugins to improve the interactivity of your blog and overall satisfaction of your readers. Although keep in mind, some of the most powerful and useful plugins are those that your readers will never even get to see.
I have listed 6 of the most essential plugins that I feel no blog should be without.
Akismet
This is THE most essential plugin you will ever require. This extremely handy plugin eliminates 99.9% of spam comments that your blog will undoubtedly receive. Akismet comes standard with every WordPress installation but to make use of its features you need to register an account at WordPress.com and insert your API key into the Akismet control panel.
Google Analytics
This plugin is one of the easiest plugins to handle and does the simple yet essential task of inserting your Google Analytics code into every one of your pages and articles on your blog.
http://wordpress.org/extend/plugins/google-analytics-for-wordpress/
XML Sitemaps
I would have to say this is one of the most essential plugins you could carry in your handy blogging toolbox. This automatically generates an updated and optimised sitemap and pings Google and all other relevant search engines of the changes made. This keeps the search engines coming back to your site to update their information.
http://wordpress.org/extend/plugins/google-sitemap-generator/
Wibiya
This is one of my favourite WordPress plugins. Wibiya is a toolbar that sits firmly at the bottom of your blog that boasts functionality such a search function for your blog, Twitter integration, Facebook integration, games, translation, and the ability to display notifications to your users. To get this amazing WordPress plugin you need to request an invitation from Wibiya themselves by simply going to their website and filling in a few details. I got my invitation in less than 24 hours and it took me a couple of minutes to set it up.
http://www.wibiya.com/
Gravatar
People like seeing pictures of themselves when they post a comment to an article. An excellent and popular way of doing this is by using Gravatar. It connects to the following avatar websites: Gravatars, OpenAvatar, Wavatar, Identicon, monsterID and MyBlogLog.
http://wordpress.org/extend/plugins/wp-gravatar/
Platinum SEO Pack
Nothing beats a seasoned SEO consultant when it comes to optimising your site, but the Platinum SEO pack does an excellent job. Install this plugin to ensure your blog stays ahead of the pack in the search engine results pages.
http://wordpress.org/extend/plugins/platinum-seo-pack/