wordsfinder

wordsfinder keyword generator could be ideal for what you are trying to do. It is free and it works on wordpress 2.5

try our tag and keyword extraction API. We belive it is better than Simple tags.

wordsfinder wordpress SEO

Le me know your thoughts. The plugin has got an API and you could use in any CMS if you wish to.

You can get an API Key from : https://www.wordsfinder.com/api_key.php