You could do it like this:
controllers.py > Root goes here, import other controllers
model.py > your app-wide sqlobjects here, import other models
forms.py > base form classes / widgets for whole app, non-module
specific forms
news/
controllers.py
model.py
forms.py
forums/
controllers.py
model.py
....
One point is that you should (I think) import any models into your root
model.py so that they can be handled by tg-admin sql commands.
I'm not sure about templates; they may need to go in a single
directory, with subdirectories for each module.
As a side note, what would be really handy would be a tg-admin command
like this:
tg-admin createapp news
which would create the required subdirectories, stub files, templates
etc in the right places in your project.