We just announced http://referencesource-beta.microsoft.com

You now can:
• Debug into .NET framework source in Visual Studio (better than before)
• Download the source with .sln and project files, so you can open and browse in Visual Studio
• Browse the source online

For a tutorial, checkout our Channel 9 video:

[View:http://media.ch9.ms/ch9/4c8f/8faf5ad6-3482-49a2-b6ee-6a61f0544c8f/HowToUseTheNetSourceBrowser_high.mp4]

For further info, see:
http://blogs.msdn.com/b/dotnet/archive/2014/02/24/a-new-look-for-net-reference-source.aspx
http://www.hanselman.com/blog/AnnouncingTheNewRoslynpoweredNETFrameworkReferenceSource.aspx