MrX

.NET Extensions Methods Library for C# and VB.NET (ASP.NET, MVC, SL, WPF, EF)
A Cloud Storage Programming Interface - Store everything
AvalonDock
CodePlex Publishing Plugin
ElasticObject - An expandable dynamic object for .NET 4.0
Extended WPF Toolkit™ Community Edition
Generic Object Storage Helper for WinRT
Google Reader .NET API
HTC Home for Windows
Html Agility Pack
NXT.NET for LEGO Mindstorms
Odyssey WPF Controls
Shazzam Shader Editor
SkyDrive .Net API Client
smtp4dev
Snoop, the WPF Spy Utility
The Windows Phone Toolkit
WPF 4.0 Chromium WebBrowser
WPF Contrib
XamlTune