Cycle through divs?

Answer 1

$('a').click(function(){
    $('.boxes').filter(':visible').hide().next().add('.boxes:first').last().show();
});

Answer 2

$('a').click(function() {
    var visibleBox = $('#container .boxes:visible');
    visibleBox.hide();
    var nextToShow = $(visibleBox).next('.boxes:hidden');
    if (nextToShow.length > 0) {
        nextToShow.show();
    } else {
        $('#container .boxes:hidden:first').show();
    }
    return false;
});

Live demo.