A list of tested plugins I DO NOT recommend.
Broken Links Checker: Although I liked this plugin, I found that it can slow performance on a site. GoDaddy even blacklisted it from their Managed WP Hosting. Rely on human editing or use this link checker.
WordPress Zero Spam: Yes, it blocks spam comments, unfortunately, I found that is was blocking all comments, including comments from registered users and users with previously approved comments. When commenting, it returns an error message that didn't really explain what the issue was so to the user it appears as though the site is broken.