If you are an ISV and are constantly working on refining your toolset, your frameworks or even your software factory, Check out the april 2007 release of Enterprise Library 3.0, it includes: Caching Application Block, Cryptography Application Block, Data Access Application Block, Exception Handling Application Block, Logging Application Block, Policy Injection Application Block, Security Application Block and Validation Application Block.
From the .NET Patterns & Practices Team :
http://msdn2.microsoft.com/en-us/library/aa480453.aspx
Philippe