What data does a 404 error page provide?

A lot of people seem to think that a 404 page is a dead end street. It's not, there's a whole lot of data that can help you find the content your visitor was looking for. Let's start with the URL: it contains something very useful. All the text that's there after the slash of your domain should be pointing you to what it is the person was looking for.

Great and detailed tutorial on how-to create better 404 pages for wordpress