C# code to class diagram

I have a C# solution which has 2 projects in it and I need to generate class diagram from code.

I know there is a built-in diagram tool in visual studio, but I'm using 2010 express and it doesn't have that. Is there any free software that is able to create that? I'm looking only for picture of class hierarchy, nothing more.

Solution

Try NClass it's cool in short , I have tried it myself.

Features:

Simple User Interface.
Free UML class diagram tool specially for C#.
From diagram to Code generation.
Classic style class diagrams.
Visual Studio style class diagrams ;)

Nclass Class Diagram Tool

NOTE: If you are a student then your school or university can provide you Visual Studio Professional edition through dreamspark program.