The Intro to WSA article that we published today is one of my favorite articles that we have published recently.  Felipe, Chris and Don worked on this piece for a long time and it does a nice job of explaining the underlying rationale for the Web service architecture that has been developed with the various WS-* specs and how the specs fit together.  We have had a couple pieces that have tried to accomplish similar things in the past with varying levels of success but this is the best one yet.  Add it to your favorites.