<table>
        {% for d in data %}
            {% if forloop.counter0|divisibleby:"2" %}<tr>{% endif %}
            <td>{{d}}</td>
            {% if forloop.counter|divisibleby:"2" %}</tr>{% endif %}
        {% endfor %}
        {% if data|length|divisibleby:"2" %}{% else
%}<td>&nbsp;</td></tr>{% endif %}
        </table>

It's a little awkward, and doesn't generalize to more than two columns,
but it does produce properly structured HTML.

If you're willing to add some code to your view, you can get more columns:

In the view:

    context['data'] = data
    ncols = 3
    for i, d in enumerate(data):
        d.firstcol = (i % ncols == 0)
        d.lastcol = (i % ncols == ncols-1)
    context['data_blanks'] = [None]*((ncols-len(data)%ncols)%ncols)

In the template:

        <table>
        {% for d in data %}
            {% if d.firstcol %}<tr>{% endif %}
            <td>{{d}}</td>
            {% if d.lastcol %}</tr>{% endif %}
        {% endfor %}
        {% for blank in data_blanks %}<td>&nbsp;</td>{% endfor %}
        {% if data_blanks %}</tr>{% endif %}
        </table>

--Ned.
http://nedbatchelder.com