Hello everyone,
I would like to tell you about the package I created a year ago - django-admin-action-forms - that I believe many people will find useful. Right now it has all the features I initially planned and has been tested by many users over the last months.
I suppose many of you use admin site actions, but they have a notable limit, there is no way to pass any values to the action function, so the only way is to hard code them.
This is exactly what this package is solving. By using the intermediate pages with forms users can be input for any number and type of arguments, that later will be accessible inside action function.
Most of the Django forms API features and many advanced options like filter-horizontal, autocomplete and inlines are implemented, making it a very powerful tool for anyone who uses Django admin regularly. The concept is based on the default action that deletes selected objects, so it feels like a standard Django feature and seamlessly integrates with rest of the admin.
I have also prepared a very descriptive README with documentation, examples and reference, I really recommend checking it out.
If you find it useful, a star on GitHub would be appreciated. 
Should you happen to have any question or suggestion, I will be happy to answer.