sshh allows you to make a persistent tcp connection (tunnel) over an http proxy. Once you have it set up, you can make new connections from either end. Similar in concept to httptunnel but more versatile and scalable.
I was looking for a tool to make a tunnel through http-only proxy from windows to linux. After long search i found just two programs that can help - this one and GNU http-tunnel. GNU http-tunnel keep falling again and again, I never managed to make it work. And this tool works just perfectly.