While you can always visit Google and run a search for Joomla! SEO extensions, there's a better way to find modules and components for your Joomla! site. The Joomla! community maintains a large directory of extensions specifically for the CMS at http://extensions.joomla.org.
The Joomla! Extensions Directory (also known as JED) is a great starting point for finding useful extensions. The directory includes a description, contact information, user reviews, and information about the compatibility of each extension. Though you are not able to download extensions from the site, you can at least browse listings by topic, and get a good idea of the various options that are open to you. Some extensions overlap with others, some are free, some are not. Accordingly, your first step should be to look at a number of extensions and decide what combination of extensions is most suitable for your site.