Application Architecture for .NET: Designing Applications and Services
A book published by the MicrosoftPatternsAndPractices group providing design-level guidance for the architecture and design of DotNet applications and services.
PDF can be downloaded from here: http://microsoft.com/downloads/details.aspx?FamilyId=A08E4A09-7AE3-4942-B466-CC778A3BAB34&displaylang=en