These days I’ve been looking at WS-Trust. The starting point when dealing with WS-* is of course reading the right specification(s), but often examples are useful too to simply get a basic understanding of the tech while leaving the deep-in-details analisys for later in the learning process.
Well, I was googling on WS-Trust last week and found out a really nice video presentation on this topic and more generally on means of achieving message integrity and confidentiality using web services. I’m quite busy recently but I admit I looked at the whole presentation (almost 1h) even if I actually knew most of the contents… that remembered me my early approaches to webservices and message security at the university (perhaps that’s because of the italian accent of the speaker 
). I think developers beginning with WS and security might found this a nice clip, good to get an idea of how low level cryptography is used as the building block for higher level specs like WS-Trust.
http://channel9.msdn.com/shows/Going+Deep/Vittorio-Bertocci-WS-Trust-Under-the-Hood/
P.S. despite being on a msdn host, there’s almost nothing specific to Microsoft there