Performance tips for the BCL
This is a good article on performance tips of the .NET Framework Base Class Library - http://msdn.microsoft.com/msdnmag/issues/06/01/CLRInsideOut/default.aspx. I learned something new about lock-free tracing and DateTime comparisons.
The great numerical comparisons of generic Vs non-generic collections, for reference and value types, is a good read. Generics (as expected) perform better than their non-generic counterparts.