Allows you te set a page to be used as the 404 page. In order for the plugin to work you need to make some modifications to the <code>404.php</code> file in your theme. I set it this way so that the 404 page could be formatted to fit the theme, or can be set more dynamically.
For more information and sample code: http://www.reitzdesigns.com/2010/08/dynamic-404-page-wordpress-plugin/
Although this plugin will work with WordPress 2.8, it’s better suited for version 3.x.

Dynamic 404 Page

Allows you to select a page to use as the content of your 404 page.

Jeffrey Carandang

Did you know that : 
<ul>
<li>It’s best to use 301 redirects for better SEO</li>
<li>It’s okay to serve a 404 when the page doesn’t exist anymore</li>
<li>404s should not always be redirected.</li>
<li>404s should not be redirected globally to the home page.</li>
<li>404 pages are normal 🙂</li>
</ul>
If you want to improve your WordPress 404 page handling and avoid SEO effects on your “404 Page Not Found” links, just install this WordPress 404 plugin and it’ll take care of your 404s 😉
<h3>Why does Forty Four stand out from the rest?</h3>
Super Lightweight WordPress 404 Page 
Forty Four Plugin creates custom page design that you can modify easily on Appearance > 404 Page. It doesn’t load the unnecessary scripts, css, images and other links to 404 page. Visitors shouldn’t have to wait too long for the page to load if it’s not available! By doing this approach you’ll lessen the requests and loading time.
Modern Custom 404 Page Design 
If you want better, responsive and modern 404 page design you should definitely install Forty Four! Of course you can upload your own background image and change the color scheme! Time to ditch your default theme 404 page 😉
Visit Logs 
All 404 links visited on your sites are available on Appearance > 404 Page: Logs. You can check the 404 links and how many times the pages were viewed.
Custom Redirects 
You can also add custom redirect for each links on Appearance > 404 Page: Logs. Not just 301 which is very recommended for SEO purposes, 302 and 307 redirect type is also available. There’s no need for additional WordPress 404 to 301 Plugin!
<blockquote>
Looking for more features? Upgrade to <a href="https://phpbits.net/plugin/forty-four/" rel="nofollow ugc">Forty-Four Pro</a> to get the complete WordPress 404 Plugin Features.
<ul>
<li>Logo Branding</li>
<li>Modern Pop-up Menu</li>
<li>Additional 404 Page Layout</li>
<li>Google Fonts Typography Option</li>
<li>More Detailed WordPress 404 Logs</li>
<li>User Searched Keyword Logs</li>
<li>WordPress 404 Page Visit Referrers</li>
<li>Custom Scripts Option</li>
</ul>
</blockquote>
If you like to contribute, report issue or have suggestions, you can find the development version on <a href="https://github.com/phpbits/forty-four" rel="nofollow ugc">Github</a>.
More information
<ul>
<li>Follow the developer <a href="https://twitter.com/phpbits" rel="nofollow ugc">@Twitter</a></li>
<li>Other <a href="https://phpbits.net/plugins/" rel="nofollow ugc">WordPress plugins</a></li>
</ul>

Forty Four – 404 Plugin for WordPress

Add a super Lightweight 404 Page aside from automatic 404 to 301 redirect for SEO. Check logs and assign custom redirect for each 404 page links.

Dynamic 404 Page vs Forty Four – 404 Plugin for WordPress