Is the Northwind Starter Kit from Codeplex a good starting point to learn more about how to best architect an ASP.NET application?
Is there something similar for the AdventureWorks database examples?
Northwind database was the best sample database for SQL Server 2000.
Talk about SQL Server 2005, AdventureWorks is better than Northwind. Northwind is not the best database due to few new features of analysis and reporting service of SQL Server 2005.
MSDN Book On Line (BOL) uses the AdventureWorks in all of their example and it makes it easy to follow up if proper understanding of AdventureWorks schema is developed.
However, SQL Server Compact Edition uses Northwind as sample database. So decide on basis of your version.