Where can I find .NET Framework class diagram?

.NET Framework 3.5 Common Namespaces and Types Poster

November 2007 Edition The .NET
Framework 3.5 Common Namespaces and Types Poster

Overview
The .NET Framework 3.5 Common Namespaces and Types Poster is downloadable as XPS or PDF format. There is also an XPS format file which prints over 16 letter or A4 pages for easy printing. Some assembly is required if you choose this print method.

Check this poster and see if it helps.

_{(source: msdn.com)}

and Here is the deep zoom version.

If you are bold and adventurous you can use a tool I found on CodeProject. Send the framework classes to it and, voila, after some crunching, grinding and groaning you should get a diagram from it.