Instead of listing unreliable, short-lived URLs, here is a guide to the categories of web proxies you might find on such lists and more reliable methods for unblocking Google Docs.
Because public proxies are abused by spammers, nearly all of their IP addresses are already blacklisted by Google's anti-bot systems. You will likely face endless CAPTCHA loops or outright access denials. The Premium Alternative Proxy Google Docs List
If you are a network administrator, the proper way to allow Google Docs access is to configure firewall and proxy rules correctly rather than relying on workarounds. Google provides official documentation listing required hosts and ports: Instead of listing unreliable, short-lived URLs, here is