Yesterday, I blogged about custom 404 pages using htaccess. In the apache article, I hinted that you should use your framework to handle the 404 page.
This article explains how to create a custom 404 page in CodeIgniter (PHP framework).
Customizing the 404 page in CodeIgniter is really easy! However, I've read articles and forum posts which make this a difficult task. This is how you create a Codeigniter 404 page.
Go into your Application/errors directory and create a file called error_404.php. That's it. In Code Igniter 2.0+ these files are already here for you so you don't even need to create them.