If you're a fan of the MSDN Application Blocks (as I am) you'll be happy to know that the Microsoft Patterns and Practices team has released the "Enterprise Library" which packages together 7 application blocks:

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnpag2/html/entlib.asp

Here's what they say about the library:

"The patterns & practices Enterprise Library is a library 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 to use on enterprise development projects. Enterprise Library features new and updated versions of application blocks that were previously available as stand-alone application blocks. All Enterprise Library application blocks have been updated with a particular focus on consistency, extensibility, ease of use, and integration."

I suspect this topic will be blogged to death over the next few days since it's a very useful set of tools.