I don't want to deal with EF, but I'd like a visual, automatically updated or updateable representation of my assembly's object model, denoting relationships with other classes in the model, like the EF model but not related to persistence. It seems like this should exist, but the only things I can find are highly manual or assuming you want to persist all your objects. I definitely do not want to pay for something.
Is there something like that that I am missing?
I am pretty sure that the "View Class Diagram" option is available in all Visual Studio 2010 edtions. Here is another thread about it: Visual Studio 2010 Professional: class diagram tool
Just check if you have it on your context menu.
Not that you will have to explicitly tell the tool to show associations such as aggregated classes, it will only show inheritance by default.
The "Class Diagram" is what you are looking for. If this is only available in VS Ultimate, then you might be out of luck. It kind of makes sense though, because the ultimate version is supposed to have all of the "planning" tools (architecture explorer, and other UML features).
There are less expensive solutions from modeling vendors, such as ModelMaker,