Few links on django best practices and on creating django reusable apps in particular:

http://lincolnloop.com/django-best-practices/index.html
http://stackoverflow.com/questions/1419442/how-to-model-a-foreign-key-in-a-reusable-django-app

The discussion on how to support multiple settings (first link) is especially interesting, because django doesn’t give any clue on how to create such configurations.

Personally I ended up using dj-skeletor app from github: https://github.com/senko/dj-skeletor, which basically has a special settings folder, one base settings file, and then specific setting files that import everything from base. To use either of them, you just symlink the right file to local.py.