Shows the most basic walkthrough of ACS. It shows how to use ACS with ASP.NET MVC, Windows Identity Foundation, and web identity providers (e.g. Live ID, Google, Yahoo!, etc.).
Here's an interview with Vittorio that discusses some of the key features of ACS.
AD FS 2.0 Integration (Active Profile)
This screencast shows how to connect a REST web service to an enterprise identity provider like AD FS 2.0. It is slightly dated (I refer to the team as .NET Services, which is no longer the case), but the capability shown in it still works with this version