Yesterday, 20th April 2010, Microsoft Patterns and Practices team announced final release of Enterprise Library v5.
About Enterprise Library:
Microsoft Enterprise Library 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.
You can download the Enterprise Library v5 with or without source code from codeplex site.