Adding elements via sidebar.php template

I’m familiar with blogger.com & Typepad templates, but I’m new to WP templates. I want to make sure not to screw things up as I add items like Amazon & Google ads.

Below, you’ll find the beginning of my sidebar template code. If I want to add an item before Archives or before
Recent Entries (for example) where should they go?

</div>

<div id="sidebar">

<ul>
<?php wp_list_pages('title_li=<h2>' . __('Pages') . '</h2>' ); ?>
<!--
<li>
<h2><?php /*_e('Archives'); */?></h2>

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

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

<ul>
<?php wp_list_cats(); ?>
</ul>
</li>
<li>
<h2>Recent Entries</h2>

<ul>
<?php $posts =
get_posts('numberposts=10');

foreach ($posts as $post) :

start_wp();

?>