后台代码：

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;
using System.Net;
using System.IO;
using System.Collections;

public partial class _Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
           
        }
       
    }

    protected void Button1_Click(object sender, EventArgs e)
    {
        TextBox2.Text = "";
        string web_url = this.TextBox1.Text;//"http://blog.csdn.net/21aspnet/"
        string all_code = "";
        HttpWebRequest all_codeRequest = (HttpWebRequest)WebRequest.Create(web_url);
        WebResponse all_codeResponse = all_codeRequest.GetResponse();
        StreamReader the_Reader = new StreamReader(all_codeResponse.GetResponseStream());
        all_code = the_Reader.ReadToEnd();
        the_Reader.Close();
        ArrayList my_list = new ArrayList();
        string p = @"http://([w-]+.)+[w-]+(/[w- ./?%&=]*)?";
        Regex re = new Regex(p, RegexOptions.IgnoreCase);
        MatchCollection mc = re.Matches(all_code);

        for (int i = 0; i <= mc.Count - 1; i++)
        {
            bool _foo = false;
            string name = mc[i].ToString();
            foreach (string list in my_list)
            {
                if (name == list)
                {
                    _foo = true;
                    break;
                }
            }//过滤

            if (!_foo)
            {
                TextBox2.Text += name + "n";
            }
        }
    }
}

前台
<%@ Page Language="C#" AutoEventWireup="true"  CodeFile="Default.aspx.cs" Inherits="_Default" %>

http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

http://www.w3.org/1999/xhtml" >