Have a look at http://codex.wordpress.org/Function_Reference/get_categories and http://codex.wordpress.org/Template_Tags/wp_list_categories
You can define the number of categories to get, also note that wpjb_form_get_categories
isn't defined by wordpress, so you may have to modify that function to add this capability.
<ul>
<?php
$args = array(
'orderby' => 'name',
'number' => 10
);
$job_categories = get_categories( $args );
foreach ($job_categories as $cat) :
?>
<li><a href="/jobs/find/?query=&category=<?php echo $cat['value']; ?>"><?php selected($cat['value'], $param["category"]); ?><?php echo $cat['description']; ?></a></li>
<?php endforeach; ?>
</ul>