Old story but a good resource

From the same people who brought you Process Explorer comes Power Collections, a .NET assembly containing many standard generic collections not implemented in the framework. These collections also have many more useful methods (NthLargest I likes) you also won't find in the standard collections. And its all free for commercial use. For the specs, see http://www.wintellect.com/PowerCollectionsAttachments/POWERCOLLECTIONS_SPECIFICATION_2.pdf