WordPress SEO plugin forces you to select a focus keyword when you are writing your articles/posts, and then makes sure that you use that selected keyword everywhere.
1) WordPress SEO by Yoast
This SEO plugin is highly suggested plugin by most of the bloggers. This plugin has the superior ability to analyse the keywords most efficiently. The users need not to go through the targeted adword program by the Google. It has a feature to measure the keywords density; with the higher density of a keyword, there are more chances of your website to appear in the search results whenever that particular keyword is searched on the internet world.
Download It From Here (http://wordpress.org/plugins/wordpress-seo/)
2) All in One SEO Pack
This SEO plugin contains a variety of features which Optimizes your WordPress blog for Search Engines. All in one SEO pack provides features like Support for Custom Post Types, Google Analytics support, Advanced Canonical URLs, Fine tune Navigational Links, Built-in API so other plugins, Generates META tags automatically, Optimize your title for search engines and Avoids the typical duplicate content found on WordPress blogs.
Download It From Here (http://wordpress.org/plugins/all-in-one-seo-pack/)
3) SEO Extended
SEO Extended is an extension to WordPress SEO by Yoast. SEO extended has divided the complete process in to two parts. With this you can edit meta keywords and post titles separately. It increase your efficiency in managing Meta Descriptions and SEO Titles with SEO Extended.
Download It From Here (http://wordpress.org/plugins/seo-extended/)
4) Basic SEO Pack
This SEO plugin is very simple but complete SEO Pack to make your site SEO Friendly and is widely used by most of the bloggers. With Basic SEO plugin you can optimize your site, manage the keywords and description meta tags, can set your default meta tag, can configure Search engine webmaster and can configure google analytics too.
Download It From Here (http://wordpress.org/plugins/basic-seo-pack/)
5) WP Social SEO Booster
WP Social SEO Booster plugin is highly well-liked for its automated SEO. It adds Twitter Card, Facebook Open Graph and Google Rich Snippets to your site to boost your web-sites search engine visibility. It is the only plugin which includes all different types of micro-data which are supported by Google.
WP Social SEO Booster plugin includes features like Google Rich Snippets, Google Authorship, Facebook Open Graph, Twitter Meta, Google Plus Itemprop Tags and Increase SEO Rank etc.
Download It From Here (http://wordpress.org/plugins/wp-social-seo-booster/)