[thelist] Pop up window on exit

[Rich Points]

Howdy,
I've been looking for a JavaScript that renders a pop up when the user 
exits the site  I'd also like to set a cookie so it doesn't pop up twice 
in one day.  I've found some scripts that claim to do this but none of 
them seem to work, even the examples.

Can someone point me to a good JavaScript that will render a pop up and 
set a cookie on exit?

Thanks
Rich