This is easy to do in a view. For example:
from django.core.urlresolvers import reverse
def Home(request): 
    posts = Article.objects.filter(published=True).order_by('-publish') 
    site = Site.objects.get_current()
    c = RequestContext(request, { 
        'posts': [{'post': post,
                   'url': request.build_absolute_uri(reverse('blog:detail', args=[post.slug]))}
                  for post in posts]
        'site': site,
    }) 
    return render_to_response('templates/index.html', c)
Then, in your template, while you're looping with {% for postobj in posts %} you can access postobj.post and postobj.url.
If you want to do this in the template instead you can probably create your own template tag without too much trouble.