The plugins below can go a long way toward preventing your visitors from ever seeing a 404 page.
These plugins are all free and range from plugins that auatomatically redirect your visitors to ones that simply log 404 errors.
This plugin from Alex King will help notify you of any 404 errors coming up on your site. It’s a very useful plugin to use if you’re changing your permalink structure or otherwise moving things around and are worried you may have missed some things and don’t want to risk broken URLs.
The Smart 404 plugin helps eliminate 404 pages automatically. If a visitor reaches a page that will return a 404 error, this plugin searches the requested URL to see if there’s some other post that likely matches. If there’s more than one potential match, it can return a list of possible links. It goes a long way to help remedy a high bounce rate caused by 404 errors.
This widget makes it easy to embed a Google search box on your custom 404 page.
A plugin that creates more useful 404 pages.
This plugin creates a customized 404 page that includes related posts to whatever keywords appear in the requested URL.
This plugin adds a dashboard widget that displays recent 404 errors. It’s a great, unintrusive way to see if your site is returning errors.
This plugin lets you replace images returning a 404 error with a default image of your choosing. You also have the option to add a class to the img tag or hide the image entirely if it’s missing.
This plugin can be used to create a custom error page similar to the one used on Dunstan Orchard’s 1976design.com/blog. The custom page it creates is immensely useful to users, displaying the last five blog posts, a search box, and the option to report the error, among other options.
This plugin is helpful if you change the permalink structure of your blog and don’t want to lose out on incoming links going to your old pages. In addition to redirecting the visitor to the new link, it also generates a “301 Moved Permanently” error so that visitors are automatically redirected in the future (along with search engine spiders).
This plugin monitors 404 errors and lets you map them to 301 redirects. It also allows you to set a custom redirection that lets you pass a URL through to a different page, file or website. And it creates a full log of all redirections. It can be used to redirect both nonexistent pages and ones that exist and it can be set to redirect based on login status or other parameters.