Works like .hide and .show but maintains element height. Based on http://jsfiddle.net/nGhjQ/

Invisibility

(function($) {
    $.fn.invisible = function() {
		return this.each(function() {
			$(this).fadeTo(100, 0);
			$(this).css("visibility", "hidden");
		});
	};
	$.fn.visible = function() {
		return this.each(function() {
			$(this).css("visibility", "visible");
			$(this).fadeTo(100, 1);
		});
	};
}(jQuery));