<ul>

{% for tag in site.tags %}
<li>
  <h3 id="{{ tag[0] }}">{{ tag[0] }}</h3>
  {% include post_list.html tag=tag %}
</li>

{% endfor %}

<li>
  <h3 id="Untagged">Untagged</h3>
  {% include post_list.html untagged=true %}
</li>

</ul>