View source code of the .NET framework
Yesterday Microsoft released the .NET Reference Source project. This project allows you to view the source code of the .NET Framework libraries while debugging with Visual Studio 2008. The sources of all .NET base class libraries, WinForms, ADO.NET, ASP.NET and WPF are already available. The LINQ, WCF and WF sources will be added soon.
Shawn Burke from Microsoft has a detailed blog post that covers all steps on how to install, configure and use it.
After modifying the configuration I needed to restart Visual Studio to enable to “Load Symbols” menu item. It works good and quite fast and the sources are well documented. Shortly, I really like it.