Quick and easy way to cross-fade between elements in a list. If those elements contained images then you have a very simple slideshow. (Requires jQuery.)

crossfade.js

if ($('ul.crossfade').length) {
    $('ul.crossfade').each(function(){
        var ul = $(this);
        if ($('li', ul).length > 1) {
            $('li:gt(0)', ul).hide();
            var fadeSpeed = (ul.attr('data-fadespeed') !== undefined ? ul.attr('data-fadespeed') : 1000);
            var nextSpeed = (ul.attr('data-nextspeed') !== undefined ? ul.attr('data-nextspeed') : 5000);
            setInterval(function(){
                $('li:first', ul)
                    .fadeOut(fadeSpeed).next('li')
                    .fadeIn(fadeSpeed).end()
                    .appendTo(ul);
            }, nextSpeed);
        }
    })
}

crossfade.js.css

ul.crossfade {
    position:relative;
    list-style-type:none;
}
ul.crossfade li {
    position:absolute;
    left:0;
    top:0;
}
ul.crossfade li:first-child ~ li {
    display:inline;
}