In the Linked In .NET Developers group, someone posted a question asking about a good open source tree structure in C#. I suppose if you use a library it does shouldn’t matter what .NET language you use. I got to thinking about how little I new of various collection type libraries for .NET. I am think along the lines of stuff like Boost and STL for C++. Well, maybe not that big. Here is a couple that I got from the discussion.
C5 Generic Collection Library
MIT-style open license