http://www.codeplex.com/AppArchGuide

From the site, you can download a great resource if you design, develop, architect or want to learn more about .Net application development.

“provides design-level guidance for the architecture and design of applications built on the .NET Framework. It focuses on the most common types of applications, partitioning application functionality into layers, components, and services, and walks through their key design characteristics.This guide is a collaborative effort between patterns & practices, product teams, and industry experts”