My current list of web-based proxies.
http://www.ohmyproxy.com/
https://proxify.com/
These are apparently all the same service:
http://www.safeforwork.net/
http://www.vpntunnel.net/
http://www.vtunnel.com/
Caveat: I'm not sure if these actually hide the entire session, or if they just obscure the URL to sniffers. I haven't done the research, and don't have the time. Use at your own risk.