ASP.NET:
http://www.codeproject.com/KB/aspnet/Detecting_Session_Timeout.aspx
‘HOMEPAGE’ in the above example could be referred to as the login.aspx
AJAX:
http://geekswithblogs.net/AzamSharp/archive/2008/01/05/118269.aspx
JAVASCRIPT:
Detecting Session Timeout and then using javascript to provide a warning regarding timing out
http://classicasp.aspfaq.com/general/how-do-i-warn-people-when-their-session-is-about-to-expire.html
SQL:
Using SQL to maintain Session information:
http://classicasp.aspfaq.com/general/how-do-i-count-the-number-of-current-users/sessions.html
Using the Ad-rotator control to server blank png to renew session.
http://forums.asp.net/t/1191063.aspx