Microsoft Shared Source Home Page
http://www.microsoft.com/resources/sharedsource
CodePlex
http://www/CodePlex.com
CodePlex is Microsoft's community development Web site. You can use CodePlex to create new projects to share with your fellow developers around the world, join others who have already started their own projects, or use the applications on this site and provide feedback.
GotDotNet.com
http://www.gotdotnet.com/Default.aspx
.NET Framework community website.
Port25
http://port25.technet.com/ Shared Source and Permissive License Projects
Shared Source Common Language Infrastructure
http://www.microsoft.com/downloads/details.aspx?FamilyId=8C09FD61-3F26-4555-AE17-3121B4F51D4D&displaylang=en
The Shared Source CLI is a compressed archive of the source code to a working implementation of the ECMA CLI and the ECMA C# language specification. This implementation builds and runs on Windows XP.
IronPython
http://www.codeplex.com/Wiki/View.aspx?ProjectName=IronPython
IronPython is the code name of the new implementation of the Python programming language running on .NET. It supports an interactive console with fully dynamic compilation. It is well integrated with the rest of the .NET Framework and makes all .NET libraries easily available to Python programmers, while maintaining full compatibility with the Python language.
Atlas Control Toolkit
http://www.codeplex.com/Wiki/View.aspx?ProjectName=AtlasControlToolkit
Built upon the ASP.NET "Atlas" Framework, the Toolkit aims to be the biggest and best collection of web-client components available.
WiX
http://wix.sourceforge.net/
The Windows Installer XML (WiX) is a toolset that builds Windows installation packages from XML source code. The toolset supports a command line environment that developers may integrate into their build processes to build MSI and MSM setup packages.

pers. addition...
Also handy dandy:
http://www.codeproject.com/
http://sourceforge.net/index.php

Read more:
http://blogs.msdn.com/kaevans/archive/2006/08/14/699593.aspx