Dynamic class for widget element

Hi,

I don’t know the best way to explain this, so I will try my best.

Usually we register a sidebar with a code like this

register_sidebar(
		array(
	 		'name' => 'Secondary Widget Area',
	 		'id'=> 'secundary_sidebar',
	 		'before_widget' => '<div class="widget">',
			'after_widget' => '</div>',
			'before_title' => '<h3 class="widgettitle">',
			'after_title' => '</h3>',
		)
	);

And when we use it, it will generate this HTML:

<div class="widget">
<h3 class="widgettitle">
......

So, my question is. How can I generate automatically a specific class name in my widget?

The reason is for me to be able to style my widgets easily.

Thanks!