using System;
using System.Net;

class NetDemo
{
    public static void Main()
    {
        HttpWebRequest req = (HttpWebRequest)WebRequest.Create("http://www.penisbot.ru");
        HttpWebResponse resp = (HttpWebResponse)req.GetResponse();
        Stream istrm = resp.GetResponseStream();
        /*теперь у нас в потоке код html-документа*/
        ...

public static void Main()
    {
        HttpWebRequest req = (HttpWebRequest)WebRequest.Create("http://yandex.ru");
        HttpWebResponse resp = (HttpWebResponse)req.GetResponse();

        StreamReader sr = new StreamReader(resp.GetResponseStream(), Encoding.GetEncoding(1251));
        StreamWriter sw = new StreamWriter(req.GetRequestStream(), Encoding.GetEncoding(1251));

        sw.Write("GET / HTTP/1.0\r\nAccept: */*\r\nAccept-Language: ru\r\nUA-CPU: x86\r\nHost: yandex.ru\r\nConnection: Keep-Alive\r\n\r\n");

        string source = sr.ReadToEnd();
        Console.WriteLine(source);
        sr.Close();
        sw.Close();
        Console.ReadLine();
    }