Coke vs. Pepsi, Apple vs. Google

The web would be a much better place if just the 404 error messages had custom pages (of course, having them for the other errors is good, too). On both my blog and my office web site that I maintain, I offer a 404 page that is not only harmonious with the look of my site, but also includes two things I think are very important components of a 404 page: the search box and a general navigation menu. Even better (though I don't have this for not knowing how to program it) is a short list of things the engine thinks perhaps you were looking for.