Windows Azure AppFabric provides both an Enterprise Service Bus in the cloud as well as cloud based authentication and authorization (think federation – ala ADFS). There’s a good introduction to the AppFabric (here), but it uses the CTP version of the App Fabric SDK. It also took me awhile to figure out that I needed to install the AppFabric SDK separately from the Azure Development Tools install.
As I said, the training above on the AppFabric was done in December 09 on the CTP, so some things changed from then, including the ___location of the Microsoft.ServiceBus.dll file. In the CTP it was under the name of “Microsoft .NET Services SDK (November 2009 CTP)”, but the released version is available (on my 64-bit Windows 7 machine) under “C:\Program Files (x86)\Windows Azure platform AppFabric SDK\V1.0\Assemblies”
Hopefully next time I won’t have to search as hard.