WP-NofollowPost adds nofollow tags to links in a post. This is done at the content-display level, meaning you don’t have to go back and apply this plugin to old posts. All posts will automatically display all links with nofollow tags in them after enabling this plugin.

It’s a really simple process and only takes a few lines of code; some of the other nofollow plugins out there do similar but are more complex and bloated with features. That’s why I decided to write this plugin.

Get it at: http://wordpress.org/extend/plugins/wp-nofollowpost/