Your best bet with a large set of models is to use django modules to your advantage, and simply create a folder named models. Move your old models.py into this models folder, and rename it init.py. This will allow you to then separate each model into more specific files inside of this model folder.
You would then only need to import each model into your init.py's namespace.
So, for instance, you might want to separate it into:
yourapp/
models/
__init__.py # This file should import anything from your other files in this directory
basic.py # Just an example name
morespecificmodels.py # Just an example name
managers.py # Might want to separate your manager into this
Then your init.py can just be:
from basic import * # You should replace * with each models name, most likely.
from managers import YourManager # Whatever your manager is called.
This is the structure that I use when my model files get huge, however I try to separate things into more pluggable apps as often as possible - so this is rarely used by me.
Hope this helps.