ThemeShock

Custom 404, helps you customize your 404. 
From the dashboard options you’re able to modify the background, the image and the fonts color and style.
This page will show users the last post on your site, so that they may choose to follow one of this instead of leaving your page.
<h3>Features</h3>
<ul>
<li>Customizable background</li>
<li>Several Patterns</li>
<li>Multiple fonts</li>
<li>24 additional images.</li>
<li>5 Different languages</li>
</ul>

Custom 404 Error Page: Unilimited designs and colors

Custom 404, creates a 404 page that is set to the default one of your WordPress installation.
This page is fully customizable from the dashboard.

Samir Shah

Matt Calvert

This plugin issues an HTTP <code>410</code> response for URLs corresponding to content that has been permanently removed from your site. Originally created by Samir Shah, now maintained by Matt Calvert. When a post or page is deleted, the plugin logs the old URL and returns 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 Gone</code> response for resources that have been permanently removed. It informs search engines and crawlers that the content will not return, improving crawl efficiency and SEO clarity.
This plugin is actively maintained by Matt Calvert as a personal project, informed by previous professional experience with similar 410-handling logic. No proprietary or employer-owned code has been used.

HTTP 410 (Gone) responses

Sends HTTP 410 (Gone) responses for deleted content, telling search engines the page is permanently removed.

Custom 404 Error Page: Unilimited designs and colors vs HTTP 410 (Gone) responses