Wintellect’s Jeffrey Richter created the Power Threading Library containing many classes to help with threading and asynchronous programming. More information about the library’s classes can be found via Jeffrey Richter’s Concurrent Affairs column in MSDN magazine. Then there is the Yahoo! Group established to support the use of this library
On top of that, Wintellect has the Power Collections Library that extends the Base Class Library with an algorithms class and a series of new containers. Now the library has moved to CodePlex and is available with the source code. Wintellect’s Peter Golde has excellent blog going into deeper details about the library.