The following book excerpt from an upcoming OBA book  7 Microsoft® Office Business Applications for Office SharePoint® Server 2007

has a good overview of OBA patterns.

Part 2 provides a good OBA overview

http://msdn2.microsoft.com/en-us/library/bb614538.aspx

Part 2 is all about OBA patterns

http://msdn2.microsoft.com/en-us/library/bb614541.aspx

- Khawar