This is a simplified rip-off of django-registration and the built-in forms and views in contrib.auth. It requires no models and is very customizable. Saving the form creates a user with an unusable password and sends a password reset email (by default, uses the password reset template too).
You must create templates/registration_form.html and the view registration_complete. I ripped this out of my site, which has a more complicated form, so I may be missing a few other things here.