Scott Guthrie announced today that they are finally releasing the source code to the .NET Framework libraries. So far you can now browse and debug the source code for the following .NET Framework libraries:
.NET Base Class Libraries (including System, System.CodeDom, System.Collections, System.ComponentModel, System.Diagnostics, System.Drawing, System.Globalization, System.IO, System.Net, System.Reflection, System.Runtime, System.Security, System.Text, System.Threading, etc).
ASP.NET (System.Web, System.Web.Extensions)
Windows Forms (System.Windows.Forms)
Windows [...]
Tags: .net