fonts awesome!

font-awesome

HTML

<link rel="stylesheet" href="http://fortawesome.github.io/Font-Awesome/assets/font-awesome/css/font-awesome.css">
<ul id="category-tabs">
    <li><a href="javascript:void"><i class="fa fa-plus-circle"></i>Category 1</a>
        <ul>
            <li><a href="javascript:void">item 1</a></li>
            <li><a href="javascript:void">item 2</a></li>
            <li><a href="javascript:void">item 3</a></li>
        </ul>
    </li>
</ul>

JavaScript

$('#category-tabs li a').click(function(){
    $(this).next('ul').slideToggle('500');
    $(this).find('i').toggleClass('fa-plus-circle fa-minus-circle');
});