I recently posted another common design pattern. It is called the Sync-Async pattern. This pattern consists of a client making a request to a server service for information, whereby the client will provide an endpoint for the server to send that information to, in an asynchronous response. However, the client also requires an immediate technical acknowledgement from the server service, within the same synchronous connection that the client has established, to be assured that the request has been well received. An example of this scenario is RosettaNet – where a client initiates a PIP3A4 Managed Purchase Order request, and the server sends back a PIP3A6 order status update (Distribute Order Status) some time later.

The post can be found here - http://blogs.msdn.com/b/appfabriccat/archive/2010/10/16/biztalk-patterns-part-2-sync-async.aspx