Arcath

Supplies filters
Orignal use case was WordPress themes that used images from facebook which in schools was blocked. By proxying the image through wp-camo images from Facebook will now load in school.

WP-Camo

Passes images through the WordPress site to prevent mixed content errors and bypass local filtering.

Greg - SiteOrigin

I built this plugin to help ease the transition during a DNS changeover, but you can use it any way you please. It turns your WordPress installation into a very simple proxy server. It fetches content from another URL, caches it and displays it. Requests are cached for 24 hours.
Install the plugin, then head over to Settings > Simple Proxy in your WordPress admin. Enter the URL you want to proxy to and when you’re ready to go, also check the enabled checkbox.
You need to have <a href="https://codex.wordpress.org/Using_Permalinks#Choosing_your_permalink_structure" rel="nofollow ugc">pretty permalinks</a> enabled.
Sign up to <a href="http://eepurl.com/hbvhM" rel="nofollow ugc">our newsletter</a> for news and updates.

Simple Proxy

Turns your WordPress installation into a simple caching proxy.

WP-Camo vs Simple Proxy