Segnalo che è stata rilasciata la versione 4.0 della Enterprise Library, una raccolta di application block molto utili (perlomeno sotto l'aspetto didattico) per lo sviluppo di applicazioni enterprise.
La potete scaricare da questo indirizzo:  http://www.microsoft.com/downloads/details.aspx?FamilyId=90DE37E0-7B42-4044-99BE-F8ECFBBC5B65&displaylang=en

Se poi volete approfondire vi consiglio:
- Documentazione sul sito MSDN: Enterprise Library 4.0 – May 2008
- Progetto su codeplex: Enterprise Library
- Un progetto che racchiude delle utili estensioni (MySql, validators ecc): Enterprise Library Contrib
- Sito Pattern and Practice: patterns and practices developer center

A titolo informativo vi riporto l'elenco degli application block inclusi (fonte MSDN):

Enterprise Library 4.0 – May 2008 contains the following application blocks:

• Caching Application Block. Developers can use this application block to incorporate a cache in their applications. Pluggable cache providers are supported.
• Cryptography Application Block. Developers can use this application block to incorporate hashing and symmetric encryption in their applications.
• Data Access Application Block. Developers can use this application block to incorporate standard database functionality in their applications.
• Exception Handling Application Block. Developers and policy makers can use this application block to create a consistent strategy for processing exceptions that occur throughout the architectural layers of enterprise applications.
• Logging Application Block. Developers can use this application block to include standard logging functionality in their applications.
• Policy Injection Application Block. Developers can use this application block to implement interception policies that can be used to streamline the implementation of common features, such as logging, caching, exception handling, and validation, across a system.
• Security Application Block. Developers can use this application block to incorporate authorization and security caching functionality in their applications.
• Unity Application Block. Developers can use this application block as a lightweight and extensible dependency injection container with support for constructor, property, and method call injection.
• Validation Application Block. Developers can use this application block to create validation rules for business objects that can be used across different layers of their applications.

Enterprise Library also includes a set of core functions, including configuration, instrumentation, and object creation. These functions are used by all other application blocks.