Uri site = new Uri("http://www.herhangibiradres.com");

WebRequest myWebRequest = WebRequest.Create(site);
WebResponse myWebResponse = myWebRequest.GetResponse();

//Site dili eğer utf-8 ise değiştirmen gerekli.
Encoding enc = Encoding.GetEncoding("windows-1254");

Stream st = myWebResponse.GetResponseStream();
StreamReader sr = new StreamReader(st, enc);

string html = sr.ReadToEnd();

Response.Write(html);