Here is a small code snippet to accomplish it:

        string str = TextBox1.Text;// some text like "go to http://blog.digvijay.eu"
        string patten = @"(http://|https://|[])+([\w-]+\.)+[\w-]+(/[\w- ./?%&=]*)?";
        Regex chr = new Regex(patten, RegexOptions.IgnoreCase);
        Match m;
        for (m = chr.Match(str); m.Success; m = m.NextMatch())
        {
            string result = m.Groups[0].ToString();
            
            // If no protocol specified it will be with "http://" as default.
            if (result.IndexOf("://") == -1)
                result = "http://" + result; 

            // you may specify nofollow and open in new window and like here
            str = str.Replace(m.Groups[0].ToString(),
            "<a href='" + result + "'  target='_blank' >" + m.Groups[0].ToString() + "</a>");

        }
        return str;

We can use a simple function as below to find all email IDs embedded in a text or html file. I just thought i could share it with everyone:

   1:          private string[] GetEmailsFromMessage(string messageBody)

   2:          {

   3:   

   4:              if (string.IsNullOrEmpty(messageBody) || messageBody.Trim().Length == 0)

   5:                  return string.Empty;

   6:   

   7:              List<string> oEmails = new List<string>();

   8:              Regex regex = new Regex(@"[a-zA-Z][\w\.-]*[a-zA-Z0-9]@[a-zA-Z0-9][\w\.-]*[a-zA-Z0-9]\.[a-zA-Z][a-zA-Z\.]*[a-zA-Z]",RegexOptions.IgnoreCase | RegexOptions.Compiled | RegexOptions.Multiline);

   9:   

  10:              MatchCollection expressionmatch = regex.Matches(messageBody);

  11:   

  12:              if (expressionmatch.Count > 0)

  13:              {

  14:                  foreach (Match m in expressionmatch)

  15:                      oEmails.Add(m.Value);

  16:              }

  17:              if (oEmails.Count > 0)

  18:                  return oEmails.ToArray();

  19:              else

  20:                  return null;

  21:   

  22:          }