I'd like to recommend a book which can be viewed as the most up-to-date comprehensive architecture guide for software applications developed using Microsoft .NET technologies. As it says in the introduction to the book: "The purpose of the Application Architecture Guide 2.0 is to improve your effectiveness when building applications on the Microsoft platform. The primary audience for this guide is solution architects and development leads. The guide provides design-level guidance for the architecture and design of applications built on the Microsoft .NET platform. It focuses on the most common types of applications and on partitioning application functionality into layers, components, and services, and also walks through their key design characteristics."
This is a must-read book for any .NET architect.
Download here.
