http://ajax.schwarz-interactive.de/csharpsample/default.aspx

Просто замечательный подход к реализации AJAX:

[Ajax.AjaxMethod]
public string Test1(string firstName, string familyName, string email, string comment)
{
  string html = "";

  html += "Hello " + firstName + " " + familyName + "";
  html += "Thank you for your comment <b>";
  html += System.Web.HttpUtility.HtmlEncode(comment);
  html += "</b>.";

  return html;
}