I've created dozens of websites using WordPress, both for my own personal use and also for clients. When I create a blog in WordPress, one of the first things I do is install plugins to turn the off the shelf version into a highly-functional, feature driven machine.
There are literally hundreds if not thousands of WordPress plugins, but I stick to a stable of 11 tried and true essential plugins to power my new blogs. Here they are.
WordPress Automatic Upgrade: WordPress updates pretty frequently, and older versions are vulnerable to hackers. WordPress Automatic Upgrade automatically updates you to the latest version of WordPress so you're site is secure and up-to-date. And believe me, the last thing you want is to find out your site is infected with malware.
Ultimate Google Analytics: Gives you access to Google Analytics so you can the lowdown on all your site traffic data (which keyword people are using to find your website to which posts are the most visited, etc) and also get in-depth insights into your blog's overall performance.
Askimet: Comes standard with every WordPress install, but you still need to activate it. Askimet protects your blog from comment spam and will delete any comments from your comment inbox that appear to be spam and are more than a month old.
Headspace: Now, some folks are partial to other SEO plugins, but I love Headspace because it enables you to easily manage a spectrum of SEO tasks. What really makes Headspace stand out are customizations options--such as the ability to drag and drop page modules (like meta tags)--to more advanced site modules, like displaying custom messages to first time visitors.
Breadcrumbs: Easily adds breadcrumb navigation to your site template, giving users more navigational choices and promotes better internal flow of link juice for SEO. NOTE: when adding the code for the breadcrumbs plugin, be sure to add it in the single.php file and immediately below <!--Begin Post--> for best results.
Robots Meta: Makes it easy to allow and disallow the search engines from indexing particular pages. You can create and edit your robots.txt and .htaccess from within your WordPress plugins dashboard and prevent dupe content and pages like internal search results and those pesky author archives from showing up in the SERPs.
Google XML Sitemap Generator: Generates a XML sitemap of your WordPress blog so it's quicker and easier for engines to find (and index) every page on your site.
WordPress Database Backup: I'm sure you backup your WordPress files regularly, right? RIGHT!?!? If not, you really want to download the WordPress Database Backup plugin, which creates backups of your core WordPress tables as well as other tables of your choice within the same database.
Linkwithin: Increase page views and user engagement with this slick related posts plugin. Linkwithin is my favorite blog widget that links to related stories from your blog archive, pulling both links AND thumbnail images.
Social Sharing Plugins: For me, it's a tossup between Share and Follow or SexyBookmarks. Bottom line is you want to include a means for users to share your content easily and these two are my favorite social bookmarking plugins. Share and Follow is more conventional, with its static row of social icons, while SexyBookmarks' sharing icons are animated when you mouse over them.
Super Cache: When Matt Cutts recommends a WordPress plugin, you should probably take heed. This plugin improves site and page speed loading time by creating a cached version of your page in HTML (without having to access PHP), which lets you serve your visitors quickly. And since site speed is now a ranking signal in the Google algos, you should do what it takes to make your blog load faster.
IMPORTANT NOTE: Make sure you update your plugins when you're prompted to in WordPress. Out-of-date plugins are vulnerable to hackers. Also, be sure to delete any unused plugins, like the crummy "Hello Dolly" plugin that comes standard. This tip is especially important if you're an affiliate marketer seeking to monetize WordPress.