You can use the toggle-event(docs) method to assign 2 (or more) handlers that toggle with each click.
Example: http://jsfiddle.net/SQHQ2/1/
$("#topbar").toggle(function(){
$(this).animate({height:40},200);
},function(){
$(this).animate({height:10},200);
});
or you could create your own toggle behavior:
Example: http://jsfiddle.net/SQHQ2/
$("#topbar").click((function() {
var i = 0;
return function(){
$(this).animate({height:(++i % 2) ? 40 : 10},200);
}
})());