经过几天研究网上的代码和谢灿大神的帮忙，今天终于用C#实现了微信公众号群发消息，现在整理一下。
总体思路：1.首先必须要在微信公众平台上申请一个公众号。
    2.然后进行模拟登陆。（由于我对http传输原理和编程不是特别懂，在模拟登陆的地方，不是特别清楚，希望有大神指教）
   3.模拟登陆后会获得一个token（令牌）和cookie。
   4.因为模拟登陆后相当于就进入了微信公众平台，在这个里面就可以抓取到需要的数据，如公众好友的昵称，fakeId。其中的fakeid非常重要，因为传输数据必须要知道                      对方的fakeid。
   5.知道对方的fakeid就可以进行数据的发送了。
我整个项目的代码在下载里面有 http://download.csdn.net/detail/zhangzhilai8/5679269
不过里面还有一些小问题，希望有人继续修改和讨论！也有人说这样会被封号，所以请谨慎操作
讲一下我项目里面的主要内容
1.WeiXinLogin.cs类是用来执行登陆功能的
 //对密码进行MD5加密
 static string GetMd5Str32(string str)
    {
        MD5CryptoServiceProvider md5Hasher = new MD5CryptoServiceProvider();
        // Convert the input string to a byte array and compute the hash.
        char[] temp = str.ToCharArray();
        byte[] buf = new byte[temp.Length];
        for (int i = 0; i < temp.Length; i++)
        {
            buf[i] = (byte)temp[i];
        }
        byte[] data = md5Hasher.ComputeHash(buf);
        // Create a new Stringbuilder to collect the bytes
        // and create a string.
        StringBuilder sBuilder = new StringBuilder();
        // Loop through each byte of the hashed data
        // and format each one as a hexadecimal string.
        for (int i = 0; i < data.Length; i++)
        {
            sBuilder.Append(data[i].ToString("x2"));
        }
        // Return the hexadecimal string.
        return sBuilder.ToString();
    }
//执行登陆操作
    public static bool ExecLogin(string name,string pass)
    {
        bool result = false;
        string password = GetMd5Str32(pass).ToUpper();
        string padata = "username=" + name + "&pwd=" + password + "&imgcode=&f=json";
        string url = "http://mp.weixin.qq.com/cgi-bin/login?lang=zh_CN ";//请求登录的URL
        try
        {
            CookieContainer cc = new CookieContainer();//接收缓存
            byte[] byteArray = Encoding.UTF8.GetBytes(padata); // 转化
            HttpWebRequest webRequest2 = (HttpWebRequest)WebRequest.Create(url);  //新建一个WebRequest对象用来请求或者响应url
            webRequest2.CookieContainer = cc;                                      //保存cookie
            webRequest2.Method = "POST";                                          //请求方式是POST
            webRequest2.ContentType = "application/x-www-form-urlencoded";       //请求的内容格式为application/x-www-form-urlencoded
            webRequest2.ContentLength = byteArray.Length;
            Stream newStream = webRequest2.GetRequestStream();           //返回用于将数据写入 Internet 资源的 Stream。
            // Send the data.
            newStream.Write(byteArray, 0, byteArray.Length);    //写入参数
            newStream.Close();
            HttpWebResponse response2 = (HttpWebResponse)webRequest2.GetResponse();
            StreamReader sr2 = new StreamReader(response2.GetResponseStream(), Encoding.Default);
            string text2 = sr2.ReadToEnd();
            //此处用到了newtonsoft来序列化
            WeiXinRetInfo retinfo = Newtonsoft.Json.JsonConvert.DeserializeObject<WeiXinRetInfo>(text2);
            string token = string.Empty;
            if (retinfo.ErrMsg.Length > 0)
            {
                token = retinfo.ErrMsg.Split(new char[] { ‘&‘ })[2].Split(new char[] { ‘=‘ })[1].ToString();//取得令牌
                LoginInfo.LoginCookie = cc;
                LoginInfo.CreateDate = DateTime.Now;
                LoginInfo.Token = token;
                result = true;
            }
        }
        catch (Exception ex)
        {
            throw new Exception(ex.StackTrace);
        }
        return result;
    }
    public static class LoginInfo
    {
        /// <summary>
        /// 登录后得到的令牌
        /// </summary>
        public static string Token { get; set; }
        /// <summary>
        /// 登录后得到的cookie
        /// </summary>
        public static CookieContainer LoginCookie { get; set; }
        /// <summary>
        /// 创建时间
        /// </summary>
        public static DateTime CreateDate { get; set; }
    }
2.在WeiXin.cs类中实现发送数据
 public static bool SendMessage(string Message, string fakeid)
    {
        bool result = false;
        CookieContainer cookie = null;
        string token = null;
        cookie = WeiXinLogin.LoginInfo.LoginCookie;//取得cookie
        token =  WeiXinLogin.LoginInfo.Token;//取得token
        string strMsg = System.Web.HttpUtility.UrlEncode(Message);  //对传递过来的信息进行url编码
        string padate = "type=1&content=" + strMsg + "&error=false&tofakeid=" + fakeid + "&token=" + token + "&ajax=1";
        string url = "https://mp.weixin.qq.com/cgi-bin/singlesend?t=ajax-response&lang=zh_CN";
        byte[] byteArray = Encoding.UTF8.GetBytes(padate); // 转化
        HttpWebRequest webRequest2 = (HttpWebRequest)WebRequest.Create(url);
        webRequest2.CookieContainer = cookie; //登录时得到的缓存
        webRequest2.Referer = "https://mp.weixin.qq.com/cgi-bin/singlemsgpage?token=" + token + "&fromfakeid=" + fakeid + "&msgid=&source=&count=20&t=wxm-singlechat&lang=zh_CN";
        webRequest2.Method = "POST";
        webRequest2.UserAgent = "Mozilla/5.0 (Windows NT 5.1; rv:2.0.1) Gecko/20100101 Firefox/4.0.1";
        webRequest2.ContentType = "application/x-www-form-urlencoded";
        webRequest2.ContentLength = byteArray.Length;
        Stream newStream = webRequest2.GetRequestStream();
        // Send the data.
        newStream.Write(byteArray, 0, byteArray.Length);    //写入参数
        newStream.Close();
        HttpWebResponse response2 = (HttpWebResponse)webRequest2.GetResponse();
        StreamReader sr2 = new StreamReader(response2.GetResponseStream(), Encoding.Default);
        string text2 = sr2.ReadToEnd();
        if (text2.Contains("ok"))
        {
            result = true;
        }
        return result;
    }
3.SendMessage.aspx.cs中主要实现获取fakeid
 public static ArrayList SubscribeMP()
    {
        try
        {
            CookieContainer cookie = null;
            string token = null;
            cookie = WeiXinLogin.LoginInfo.LoginCookie;//取得cookie
            token = WeiXinLogin.LoginInfo.Token;//取得token
            /*获取用户信息的url，这里有几个参数给大家讲一下，1.token此参数为上面的token 2.pagesize此参数为每一页显示的记录条数
            3.pageid为当前的页数，4.groupid为微信公众平台的用户分组的组id，当然这也是我的猜想不一定正确*/
            string Url = "https://mp.weixin.qq.com/cgi-bin/contactmanagepage?t=wxm-friend&token=" + token + "&lang=zh_CN&pagesize=10&pageidx=0&type=0&groupid=0";
            HttpWebRequest webRequest2 = (HttpWebRequest)WebRequest.Create(Url);
            webRequest2.CookieContainer = cookie;
            webRequest2.ContentType = "text/html; charset=UTF-8";
            webRequest2.Method = "GET";
            webRequest2.UserAgent = "Mozilla/5.0 (Windows NT 5.1; rv:2.0.1) Gecko/20100101 Firefox/4.0.1";
            webRequest2.ContentType = "application/x-www-form-urlencoded";
            HttpWebResponse response2 = (HttpWebResponse)webRequest2.GetResponse();
            StreamReader sr2 = new StreamReader(response2.GetResponseStream(), Encoding.Default);
            string text2 = sr2.ReadToEnd();
            MatchCollection mc;
            //由于此方法获取过来的信息是一个html网页所以此处使用了正则表达式，注意：（此正则表达式只是获取了fakeid的信息如果想获得一些其他的信息修改此处的正则表达式就可以了。）
             Regex r = new Regex("\"fakeId\"\\s\\:\\s\"\\d+\""); //定义一个Regex对象实例
            mc = r.Matches(text2);
            Int32 friendSum = mc.Count;          //好友总数
            string fackID ="";
            ArrayList fackID1 = new ArrayList();
            for (int i = 0; i < friendSum; i++)
            {
                fackID = mc[i].Value.Split(new char[] { ‘:‘ })[1];
                fackID = fackID.Replace("\"", "").Trim();
                fackID1.Add(fackID);
            }
            return fackID1;
   }
        catch (Exception ex)
        {
            throw new Exception(ex.StackTrace);
        }
    }

C#实现微信公众号群发消息（解决一天只能发一次的限制）