http://wordpress.org/extend/plugins/seo-booster-lite/
This plugin will detect which page on Google your post appears in and for which keywords. It then builds a sitewide widget on your blog displaying these keywords.
The strategy is that by displaying these terms, your search volume picks up and your rank for these terms increases. NOTE: Uses only terms that appear on page 2 and higher since
these are the ones that you have a higher chance of influencing with this plugin.