Microsoft release version 5.0 of it’s famous Enterprise Library. This is a collection of application blocks designed to assist developers with common enterprise development challenges. Application blocks are a type of guidance, provided as source code that can be used "as is," extended, or modified by developers for use in enterprise development projects.

Microsoft Enterprise Library 5.0 – April 2010

Download Microsoft Enterprise Library 5.0

Microsoft Enterprise Library 5.0 Documentation

Microsoft Patterns & Practices

Microsoft Patterns & Practices – Enterprise Library on CodePlex