sidebar.php

<div id="sidebar">
<h2> Sidebar area</h2>

<h2><?php _e('Categories'); ?></h2>

<ul>
<?php wp_list_cats('sort_column=name&optioncount=1&hierarchical=0'); ?>
</ul>

<h2><?php _e('Archives'); ?></h2>

<ul>
<?php wp_get_archives('type=monthly'); ?>
</ul>

</div>