Favorite Django Tips & Features?

Inspired by the question series 'Hidden features of ...', I am curious to hear about your favorite Django tips or lesser known but useful features you know of.

• Please, include only one tip per answer.
• Add Django version requirements if there are any.

I'm just going to start with a tip from myself :)

Use os.path.dirname() in settings.py to avoid hardcoded dirnames.

Don't hardcode path's in your settings.py if you want to run your project in different locations. Use the following code in settings.py if your templates and static files are located within the Django project directory:

# settings.py
import os
PROJECT_DIR = os.path.dirname(__file__)
...
STATIC_DOC_ROOT = os.path.join(PROJECT_DIR, "static")
...
TEMPLATE_DIRS = (
    os.path.join(PROJECT_DIR, "templates"),
)

Credits: I got this tip from the screencast 'Django From the Ground Up'.

Install Django Command Extensions and pygraphviz and then issue the following command to get a really nice looking Django model visualization:

./manage.py graph_models -a -g -o my_project.png