Asp.Net

Display MessageBox in Asp.net
Use javascript alert to display Message box in asp.net
eg:
Response.Write(<script>alert('Hello')</script>);

Browser Compatability

if (Request.UserAgent.IndexOf("AppleWebKit") > 0)
{
Request.Browser.Adapters.Clear();
}

LogOut(SessionEnd)

Session.Abandon();
FormsAuthentication.SignOut();
Response.Redirect("~/example.aspx");

TextBox Blur if it's Empty 
Take 1 textbox, 1button, and 1required field validator...
Using Java Script

<style type="text/css">
    .ErrorControl
    {
        background-color: #FBE3E4;
        border: solid 1px Red;
    }
    .style1
    {
        width: 368px;
    }
</style>

<link rel="openid.server" href="http://openid.example.com/" />
<script type="text/javascript">
    function WebForm_OnSubmit() {
        if (typeof (ValidatorOnSubmit) == "function" && ValidatorOnSubmit() == false)
         {
             for (var i in Page_Validators)
             {
                 try
                 {
                    var control = document.getElementById(Page_Validators[i].controltovalidate);

                    if (!Page_Validators[i].isvalid)
                     {
                        control.className = "ErrorControl";
                    } else {
                        control.className = "";
                    }
                } catch (e) { }
            }
            return false;
        }
        return true;
    }
</script>