Alex King

Crowd Favorite

If you’ve decided to move things around on your site, you might overlook a few redirects and end up with some broken URLs. This will help you catch those so you can take care of them.

404 Notifier

Log 404 (file not found) errors on your site and get them delivered to you via e-mail or RSS.

Samir Shah

This plugin will issue a HTTP <code>410</code> response to requests for articles that no longer exist on your blog. When you delete a post or page, it records the URL for that page and issues a <code>410</code> response when that URL is requested. You can also manually manage the list of obsolete URLs.
The <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html#sec10.4.11" rel="nofollow ugc">HTTP Specification</a> defines the <code>410</code> response header for use when a resource has been permanently removed. It informs robots visiting your site that the requested content has gone, and that they should stop trying to access it.
If you come across any bugs or have suggestions, please use the plugin support forum. I can’t fix it if I don’t know it’s broken! Please check the <a href="https://wordpress.org/extend/plugins/wp-410/faq/" rel="ugc">FAQ</a> for common issues.

410 for WordPress

A plugin that sends HTTP 410 (Gone) responses to requests for articles that no longer exist on your blog.

404 Notifier vs 410 for WordPress