404 Page error

I just found out that the second most popular items in our portal is the 404 page.
So i googled sites that have tips on how to create a 404 page so that it wouldn't come off as an annoying page error display, but rather a customized page informing a return to the home page or a search function, and so and so forth.

So far these were links that I found helpful:

The Perfect 404
Custom 404 Error Page
Useful "Page Not Found" error pages

So I should come up with a really reasonable 404 page. Will post it here if I'm done with it. I should really put a Site Map utility. My next on the list...