WordPress SEO by joostdevalk is a complete SEO plugin that exists today for WordPress.org users. It incorporates everything from a snippet preview that helps you optimize your page titles, meta descriptions and keywords to XML sitemaps, and loads of optimization options in between.
Feature list:
Post titles and meta descriptions
Robots Meta configuration
Canonical
Breadcrumbs
Permalink clean up
XML Sitemaps
RSS enhancements
Edit your robots.txt and .htaccess
Clean up head section
Download and info: http://wordpress.org/extend/plugins/wordpress-seo/