What happens when your users navigate to a nonexistent page?
What should happen?
Here are five interesting resources on building an excellent 404 page ("Page Not Found"):
- The Perfect 404 from A List Apart
- Creating user-friendly 404 pages from Coding Horror
- Improving the Dreaded 404 Error Message from Jakob Nielsen
- Creating an Error 404 Page from the WordPress Codex
- Correctly Creating a 404 that generates a 404 from Rocknbil at Webmaster World
The last post reminds us that "pretty" 404 pages must still return a 404 HTTP header code, so that search spiders know the page isn't really there. This subtlety was a new one to me (though not to our web team, happily.)
I also agree with JDMorgan's comment on keeping 404s simple:
Agree. Avoid the complex or cute 404s like this.