I've been trying this one out for a little while and like the results so far. It's called SEO SearchTerms Tagging 2. What it does is track your hits by what search term the visitor got there by and logs it in your WP dashboard. I like this part as it makes it easy for me to keep track of what keywords are doing well and then I can target them in my backlinking efforts. Sort of striking while the iron's hot and letting my fast dogs run so to say.
The better part is that it will let you easily add the keywords, and links to the posts that also have gotten hits for that search term, at the bottom your posts, sort of like the "related posts" plugins do. This is great because when SE's spider the page you'll get link juice for that search term, that was already working for you in the first place. I can see the list of keywords that are getting multiple hits grow every day and I'm assuming this is helping that along.
Another cool part is that it will automatically re-publish any of your posts that aren't getting any search traffic, in hopes that the fresh ping to your update services will assist it in getting some organic search hits. It lets you know how many are still to get traffic from a true search result and also tells you the last one it recently promoted for you. I can see the list dwindling even though I keep adding fresh posts to my blog every day.
Just search the bolded text above in your WP add plugins feature and you'll find it...it's free.