WordPress by default is pretty decent at letting search engines see what’s going on. But there are a whole bunch of plugins that can be used to make your blog rank better.
This plugin will create a Google sitemaps compliant XML-Sitemap of your WordPress blog. It supports all of the WordPress generated pages as well as custom ones. Everytime you edit or create a post, your sitemap is updated and all major search engines that support the sitemap protocol, like ASK.com, Google, MSN Search and YAHOO, are notified about the update.
Optimizes your WordPress blog for Search Engines: page titles, meta tags, keywords, and descriptions. This plugin allows you to configure them for either your entire blog or on a post by post basis.
Redirection is a WordPress plugin to manage 301 redirections, keep track of 404 errors, and generally tidy up any loose ends your site may have. This is particularly useful if you are migrating pages from an old website, or are changing the directory of your WordPress installation.
If you just migrated your WordPress blog from one permalink structure to another, and you don’t want to lose Pagerank or traffic that accesses your blog through the old permalinks, this is for you.
SEO Smart Links provides automatic SEO benefits for your site in addition to custom keyword lists, nofollow and much more. SEO Smart Links can automatically link keywords and phrases in your posts and comments with corresponding posts, pages, categories and tags on your blog.
This is an improvised version of the AllinOne SEO plugin. It does everything that AllinOne was doing and also some extra cool features. It takes care of pretty much everything, a bit more advanced than a basic SEO plugin but easy to use as well.