Wordpress 2.9+ plugin that prevents duplicate posts

I need a Wordpress plugin (compatible with 2.9+) created that prevents duplicate posts from publishing in our Wordpress site. I don't need to delete old posts, rather prevent duplicates from publishing. I've looked into modifying the "post.php" file, but this will only last until the next update of Wordpress. I would like a plugin that automatically checks the title and date and instead of adding "-2" or "-3" to the post, it is never published. We are using "Autoblogged" to publish content from a variety of RSS feeds, and even though the "prevent duplicate content" boxes are checked, duplicate posts always come through. Thanks! James