using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Text.RegularExpressions;


/// <summary>
/// FiterHtml 的摘要说明
/// </summary>
public class FiterHtml
{
    public FiterHtml() { }
    ///   <summary>
    ///   去除HTML标记
    ///   </summary>
    public static string NoHTML(string Htmlstring)
    {
        //删除脚本
        Htmlstring = Regex.Replace(Htmlstring, "<script[^>]*>[\s\S]*?</script>", "",
          RegexOptions.IgnoreCase);
        //删除HTML
        Htmlstring = Regex.Replace(Htmlstring, @"<(.[^>]*)>", "",
          RegexOptions.IgnoreCase);
        Htmlstring = Regex.Replace(Htmlstring, @"([\r\n])[\s]+", "",
          RegexOptions.IgnoreCase);
        Htmlstring = Regex.Replace(Htmlstring, @"-->", "", RegexOptions.IgnoreCase);
        Htmlstring = Regex.Replace(Htmlstring, @"<!--.*", "", RegexOptions.IgnoreCase);
        Htmlstring = Regex.Replace(Htmlstring, @"&(quot|#34);", "\"",
          RegexOptions.IgnoreCase);
        Htmlstring = Regex.Replace(Htmlstring, @"&(amp|#38);", "&",
          RegexOptions.IgnoreCase);
        Htmlstring = Regex.Replace(Htmlstring, @"&(lt|#60);", "<",
          RegexOptions.IgnoreCase);
        Htmlstring = Regex.Replace(Htmlstring, @"&(gt|#62);", ">",
          RegexOptions.IgnoreCase);
        Htmlstring = Regex.Replace(Htmlstring, @"&(nbsp|#160);", "   ",
          RegexOptions.IgnoreCase);
        Htmlstring = Regex.Replace(Htmlstring, @"&(iexcl|#161);", "\xa1",
          RegexOptions.IgnoreCase);
        Htmlstring = Regex.Replace(Htmlstring, @"&(cent|#162);", "\xa2",
          RegexOptions.IgnoreCase);
        Htmlstring = Regex.Replace(Htmlstring, @"&(pound|#163);", "\xa3",
          RegexOptions.IgnoreCase);
        Htmlstring = Regex.Replace(Htmlstring, @"&(copy|#169);", "\xa9",
          RegexOptions.IgnoreCase);
        Htmlstring = Regex.Replace(Htmlstring, @"&#(\d+);", "",
          RegexOptions.IgnoreCase);
        Htmlstring.Replace("<", "");
        Htmlstring.Replace(">", "");
        Htmlstring.Replace("\r\n", "");
        Htmlstring = HttpContext.Current.Server.HtmlEncode(Htmlstring).Trim();

        return Htmlstring;
    }
    public static string StripHTML(string strHtml)
    {
        string[] aryReg =
            {
              @"<script[^>]*?>.*?</script>",
              @"<(\/\s*)?!?((\w+:)?\w+)(\w+(\s*=?\s*(([""'])(\\[",
               @"'tbnr]|[^\7])*?\7|\w+)|.{0})|\s)*?(\/\s*)?>", @"([\r\n])[\s]+",
                @"&(quot|#34);", @"&(amp|#38);", @"&(lt|#60);", @"&(gt|#62);",
                @"&(nbsp|#160);", @"&(iexcl|#161);", @"&(cent|#162);", @"&(pound|#163);",
                @"&(copy|#169);", @"&#(\d+);", @"-->", @"<!--.*\n"
            };

        string[] aryRep =
            {
              "", "", "", "\"", "&", "<", ">", "   ", "\xa1",  //chr(161),
              "\xa2",  //chr(162),
              "\xa3",  //chr(163),
              "\xa9",  //chr(169),
              "", "\r\n", ""
            };

        string newReg = aryReg[0];
        string strOutput = strHtml;
        for (int i = 0; i < aryReg.Length; i++)
        {
            Regex regex = new Regex(aryReg[i], RegexOptions.IgnoreCase);
            strOutput = regex.Replace(strOutput, aryRep[i]);
        }
        strOutput.Replace("<", "");
        strOutput.Replace(">", "");
        strOutput.Replace("\r\n", "");
        return strOutput;
    }
    ///   <summary>
    ///   移除HTML标签
    ///   </summary>
    ///   <param   name="HTMLStr">HTMLStr</param>
    public static string ParseTags(string HTMLStr)
    {
        return System.Text.RegularExpressions.Regex.Replace(HTMLStr, "<[^>]*>", "");
    }
    ///   <summary>
    ///   取出文本中的图片地址
    ///   </summary>
    ///   <param   name="HTMLStr">HTMLStr</param>
    public static string GetImgUrl(string HTMLStr)
    {
        string str = string.Empty;
        string sPattern = @"^<img\s+[^>]*>";
        Regex r = new Regex(@"<img\s+[^>]*\s*src\s*=\s*([']?)(?<url>\S+)'?[^>]*>",
          RegexOptions.Compiled);
        Match m = r.Match(HTMLStr.ToLower());
        if (m.Success)
            str = m.Result("${url}");
        return str;
    }

}

测试用例:

protected void Page_Load(object sender, EventArgs e)
   {
       string test = "例：<strong   id=\"abc\">你好</strong><p><a href=\"http://www.xingzhu.net.cn\" target=\"_blank\">星烛网</a></p><IMG title=星烛网 src=\"http://121.9.206.74/Gift/face/2.gif\" border=0>H<EM>i,星烛网</EM>";
       FiterHtml filter = new FiterHtml();
       Response.Write(FiterHtml.NoHTML(test));
   }

输出结果:
例：你好星烛网Hi,星烛网