How do you extend the Site model in django?
I just used my own subclass of Site and created a custom admin for it. 
Basically, when you subclass a model in django it creates FK pointing to parent model and allows to access parent model's fields transparently- the same way you'd access parent class attributes in pyhon. 
Built in admin won't suffer in any way, but you'll have to un-register Sites ModelAdmin and register your own ModelAdmin.
What is the best approach to extending the Site model in django? Creating a new model and ForeignKey the Site or there another approach that allows me to subclass the Site model?
I prefer subclassing, because relationally I'm more comfortable, but I'm concerned for the impact it will have with the built-in Admin.