jQuery fade out then fade in

fade the other in in the callback of fadeout, which runs when fadeout is done. Using your code:

$('#two, #three').hide();
$('.slide').click(function(){
    var $this = $(this);
    $this.fadeOut(function(){ $this.next().fadeIn(); });
});

alternatively, you can just “pause” the chain, but you need to specify for how long:

$(this).fadeOut().next().delay(500).fadeIn();