If you have not visited Google’s Webmaster Central website you should, they have a bunch of tools to help websites and web developers. Today on the Google Webmaster Central Blog there was an excellent article on how to make your 404 pages more useful.
Instead of just displaying the standard 404 message, Google gives you some code to insert that will display more useful information including potential matches to the page the user was looking for. Below is a demo screen shot of an enhanced 404 page.
Nifty. Often, a 404 is the worst part about a website. Change CMS? You’ll get loads of 404s.