Google wants to help webmasters optimize their 404 Pages and help visitors get a better experience by browsing around your site rather than leaving it. Try the Google 404 widget and enhance your 404 pages.
Google 404 widget
As I was navigating my Google Webmasters tools, I found a new experimental feature under Tools called Enhance 404 pages. Usually when a user clicks a link to a page that’s no longer available, your server returns a 404 (Page Not Found) error. Site owners and webmasters create custom 404 pages to help visitors find related content on your site. WordPress bloggers can easily create a custom 404 page.
Now webmasters can add the Google 404 widget to the custom 404 page. The 404 widget automatically provides helpful suggestions instead of error messages such as a search box for your site with appropriate search suggestions and tries to provide alternatives to incorrect URLs. Now visitors can easily find the information they need and will stay on your site longer generating more pageviews for you. See the widget at work below.
Simply cut and paste the code they provide into your 404 page template and enhance the page. This is a simple way for site owners to get a more functional 404 page. Since the widget is an experimental feature, they currently don’t provide closest match, alternative URL and sitemap suggestions for all sites.
We pasted the code on our site and it worked very well on the 404 page. But the closest match, alternative URL and sitemap suggestions were not there for our site. If you are looking to design some cool 404 pages, check out these cool 404 designs and then get more 404 ideas.