mousewheel
<script type="text/javascript">
var EventUtil = {
addHandler: function() {...},
getEvent: function(event) {...},
}
EventUtil.addHandler(document, "mousewheel", function(event) {
event = EventUtil.getEvent(event);
alert(event.wheelDelta);
});
</script>
...
Role o botão do mouse para frente e depois para trás.
Funciona somente no IE, Opera, Safari e Chrome.