JordiPlana

This plugin hooks the normal WordPress workflow in order to determine if the request is processing will cause a 404 HTTP error. In that case it prevents WordPress to do any other processing and sends the user to the page defined in the plugin options.
A working and simple solution.
For more information about this plugin you can check <a href="http://jordiplana.com/404-simple-redirect-plugin-for-wordpress" title="404 Simple Redirect Plugin for WordPress" rel="nofollow ugc">the official page</a>.

404 Simple Redirect

This plugin hooks the normal Wordpress workflow in order to determine if the request is processing will cause a 404 HTTP error.

janiko

This very simple plugin aims at avoiding mixed content when using https for wordpress sites.
<h4>Principle</h4>
When you are using HTTPS for browsing, all content resources will point to https. All ‘http’ references will be changed to ‘https’.
On the contrary, if you want HTTP browsing, all references will be changed to ‘http’, which can be useful if you are behind a proxy that filters https.

Https Switcher

Thanks @janiko for creating this great plugin! It works fantastic on my sites and even your source code looks amazing. Well done!

Simple and yet powerful!

Force http/https for resources, depending on the scheme you use.

404 Simple Redirect vs Https Switcher