This all-in-one plugin is a real benchmark for SEO (Search Engine Optimization).
See its a detailed description, to show you how this plugin is one of the best, if not the best one :
Titles: Allows rewriting the titles of articles and posting them before anything else (eg the title of your blog), which is much more relevant to a search engine. Indeed, the article title should contain keywords characteristics of your article to appear as the best in Google and Yahoo!, including results;
Description: automatically or manually created the description tag, the same one that appears in the search results below the title of the article or the site. It is therefore essential and should, again, contain keywords representative of the product to maximize its SEO;
Keywords: allows you to add tags to the same manner as provided for this purpose since WordPress 2.3 field. However, while it is preferable to a moderately tagg entry through the field of WordPress for not having a cloud of tags disproportionate (2-3 max, in my humble opinion), there are no limits in for All in One SEO Pack.
Duplicate content: the plugin handles very well the problems of duplicate content via the noindex function. It is available separately for each applicable sections or pages for archives, categories or tags.