svil4ok

Get tags on every single post (is_single()) and put them in meta keywords tag in header (wp_head()). Otherwise it’ll use the keywords define in $default_keywords. Get the_excerpt() and put it in meta description tag in header (wp_head()). Otherwise it’ll use the description define in $default_description.
Requires the wp_head() tag !

Meta Keywords & Description

gaxx

Automatically adds keywords and description meta tag on every page based on title, tags, categories, etc.
It works on the basis of defining some simple, tag-based rules for different page types (home, category, post etc).
Built on the foundations of the excellent Automated Keywords Generator by Julian Widya Perdana (http://mr.hokya.com/automated-keywords-generator)

Gaxx Keywords

Automatically adds keywords and description meta tag on every page based on rules that draw information from title, tags, categories etc

Meta Keywords & Description vs Gaxx Keywords