WordPress SEO by Yoast

This plugin is written from the ground up by Joost de Valk and his team at Yoast to improve your site’s SEO on all needed aspects. While this WordPress SEO plugin goes the extra mile to take care of all the technical optimization, more on that below, it first and foremost helps you write better content. WordPress SEO forces you to choose a focus keyword when you’re writing your articles, and then makes sure you use that focus keyword everywhere.

http://wordpress.org/plugins/wordpress-seo/

Breadcrumbs

This theme supports the built-in Breadcrumbs functionality provided by WordPress SEO by Yoast. This allows you to create an easy navigation that is great for both users and search engines and will support the search engines in understanding the structure of your site.