var http = require('http');

http.createServer(function(request, response) {
  var proxy = http.createClient(80, request.headers['host'])
  var proxy_request = proxy.request(request.method, request.url, request.headers);
  proxy_request.on('response', function (proxy_response) {
	proxy_response.pipe(response);
	response.writeHead(proxy_response.statusCode, proxy_response.headers);
  });

  request.pipe(proxy_request);
}).listen(8080);

Simpliest possible proxy server in Node.js