In Visual Studio 2005 and prior you could export your code to Visio and view the relationships between the objects and what methods, properties and fields it had. This was great
NDepend is certainly the .NET tool you are looking for. It comes with a dependency graph coupled with a dependency matrix. You can try NDepend straight on your code by downloading the free Trial Edition.
More on NDepend Dependency Graph
More on NDepend Dependency Matrix:
Disclaimer: I am part of the tool team
Do you require the software to be free? If not, you might consider a UML tool like Sparx Enterprise Architect. It can import your code, and has two add-ons that go further in terms of Visual Studio integration.
There is a decent, free version of a UML diagramming tool called Argos here http://argouml.tigris.org/features.html. Out of the box it can both forward and reverse engineer Java, I'm fairly certain there are add-ins for Visual Studio that help support forward and reverse engineering of C# code. I would look into that.
When i search for code in codeplex i found this http://vsdm.codeplex.com/ maybe help you.
You may have tried PowerDesigner, it runs under Eclipse through a plugin and it also supports Visual Studio. The only downside is that it only works on Windows.
Another application for modeling is System Architect from IBM (Popkin). It has been used by some major corporations and is still maintained.
Have you tried the PowerToys?