Here is a list of the most essential plugins to use in 2013, and what every plugin do to improve your site.
W3 Total Cache – Speeds load time of your blog.
WP SEO Yoast – A complete SEO plugin.
Sociable – Adds cool social sharing buttons on your blog.
Google XML Sitemaps – Still a must have plugin for indexing your pages.
Better WP Security – Strengths the security of your WordPress installation and site.
Contact Form 7 – Adds a nice contact form to your site.
Akismet – Still a very efficient method for fighting comment spam.
Embed Plus – Great for embedding YouTube videos into your posts.
SEO Search TermsTagging – Multiply blog traffic by strengthening on page SEO.
WordPress Firewall – monitors web requests to identify and stop the most obvious attacks.
New security vulnerabilities of WP plugins are found from time to time, so don’t forget to regularly update your WP plugins so you can stay on the safe side.