Django - Model graphic representation (ERD)

If you want to extract UML diagram from your Django models you can use the Graph models command of django-extensions. Another one that do mostly the same thing: django-graphviz.

If you want to create your Django models from UML: uml-to-django.

And to create UML diagrams, there's Dia, yED and ArgoUML

You can check also this list of tools.

Best I can think of is Argo UML which requires you to design by hand (and then you can convert the UML into Django with this tool)

If you want to do django - uml conversion (the other way) try looking at Django To UML