Picked up a quick tip over LLR for quick django admin previews. This works perfect on my projects.

Add a new preview view to your app

# views.py
from django.contrib.admin.views.decorators import staff_member_required
from django.views.generic.list_detail import object_detail

@staff_member_required 
def preview(request, object_id): 
    return object_detail(request, object_id=object_id, queryset=Article.objects.all(), 
        template_object_name = 'article', )

We now just add a new URL to call the view

# urls.py
(r'^admin/-appname-/article/(?P<object_id>[0-9]+)/preview/$', 
    'apps.-appname-.views.preview'),

Now edit the admin change_form template to add a preview button

# templates/admin/-appname-/article/change_form.html
{% extends "admin/change_form.html" %} {% load i18n %}
 {% block object-tools %}
 {% if change %}{% if not is_popup %}
   <ul class="object-tools">
     <li><a href="history/" class="historylink">
         {% trans "History" %}</a></li>
     <li><a href="preview/" class="viewsitelink" target="_blank">
         {% trans "View preview" %}</a></li>
   {% if has_absolute_url %}<li>
     <a href="../../../r/{{ content_type_id }}/{{ object_id }}/" class="viewsitelink">
         {% trans "View on site" %}</a></li>{% endif%}
   </ul>
 {% endif %}{% endif %}
 {% endblock %}

Done and done. Obviously the file has to be saved before you can actually preview it. I have an 'active' or 'published' boolean field on my model that I keep unchecked until its been previewed.

References:

http://latherrinserepeat.org/2008/7/28/stupid-simple-django-admin-previews/