Konstantin Sokolov

Performs automatic keyword extraction. Adds a keyword taxonomy for browsing and a keyword extraction metabox in the post editing page. 
Available in English and Mandarin.

Eventflow Keyword Extraction

Automatic keyword extraction for SEO enhancement and improved user experience.

Steve

This plugin uses custom fields to allow the page title tag to be customised and differ from the actual page title.
Both meta descriptions and keywords can also be added if required.
Page meta details can be modified on any publicly accessible post type, such as posts and pages, as well as custom post types.
Theme and plugin developers should note that it is possible override the page title within your templates by setting <code>$wppm_title = 'Newly defined title';</code> before the call to <code>get_header();</code>.

Page Meta

Adds the ability to override the page meta title and add in meta descriptions and keywords for pages.

Eventflow Keyword Extraction vs Page Meta