Kaspars

Set any page to be used as the 404 error page under “Settings > Reading”.

Custom 404 Error Page

Use any static page as the 404 error page.

Matt Royal

This plugin dynamically creates pages for the most common error codes. It generates page templates for each error code from within your themes current page.php template file and assigns each new page template to the appropriate error page. It then updates your HTACCESS file with the correct references to these new pages.
Requires WordPress 3.0 +
Get in touch with me at: 
http://mattroyal.co.za/
Features
<ul>
<li>Dynamically creates all required pages</li>
<li>Creates page tempaltes and automatically asigns them to the newly created pages</li>
<li>Updates your HTACCESS file with the required commands to make the pages display when needed.</li>
</ul>
<h3>Usage</h3>
<ul>
<li>Enable the Plugin</li>
<li>Ensure your HTACCESS file and theme folder are writable</li>
<li>Check that pages have been created</li>
<li>Disable the plugin</li>
</ul>
Please Note – NB!!
<ul>
<li>In the event of moving your WordPress installtion into another directory, please note you will need to delete your HTACCESS file and resave it again.</li>
<li>Do not change the slugs/Permalinks of the newly created pages. If you do so you will have to update the new slugs within the HTACCESS file as well.</li>
</ul>

WordPress Easy Custom Error Pages

This plugin dynamically creates pages & page templates for the most common error codes/statuses and updates your HTACCESS file as required to work …

Custom 404 Error Page vs WordPress Easy Custom Error Pages