I've seen that VS 2010 Ultimate can generate model graph from existing code. But VS 2010 Ultimate version costs 11K US$, way too much for my budget. Is there any good alternative to do graph visualization of .NET code?
NDepend comes with a dependency graph coupled with a dependency matrix. You can try NDepend straight on your code thanks to a Free Trial Edition. Read more about this feature in this article Exploring Existing Code Architecture in Visual Studio. Any kind of graph is supported including:
Here are screenshots for illustration: