3👍
I have actually been doing the same project lately. The admin site doesnt really know how to represent the non-relational style elements that are present in a mongodb document, so you would have to define custom field/widgets. Refer to this part of the documentation which explains how to extend your ModelAdmin to specify overrides.
https://docs.djangoproject.com/en/1.3/ref/contrib/admin/#modeladmin-objects
For list types for instance, django has no way to know what type of values the list contains and how to represent them.
As for a visual mongodb manager, not sure what OS you are on, but Im on OSX and I love this one: http://mongohub.todayclose.com/
Otherwise, here is a list of other management options: http://www.mongodb.org/display/DOCS/Admin+UIs
Take your pick for either an OS native or web based.