Example 1:

$('a').click( function() {
	if( this.hostname && this.hostname !== location.hostname ) {
		window.open( $(this).attr('href') );
		return false;
	}
});

This first example just opens the link in a new window any time the link is to an external domain.

Example 2:

var h = window.location.host.toLowerCase();
$("a[href^='http']:not([href^='http://" + h + "']):not([href^='http://www." + h + "']):not([href^='https://" + h + "']):not([href^='https://www." + h + "']):not([href^='mailto']), a[href$='.pdf']").attr("target", "_blank").append(' »');

This next example opens the link in a new window if the href attribute points to an external domain, but is not a mailto: link or a link to a PDF document.