http://robrelyea.com/xaml/docs takes you right to the MSDN documentation on the Xaml Language.

http://robrelyea.com/xaml/editors takes you to a list of WPF centric Xaml Editors.

http://robrelyea.com/xaml/spec takes you to the current public Xaml Object Mapping Specification.

Chuck Jazdzewski is an Architect who has made major contributions to Xaml. Chuck's posts about Xaml.  (Read in reverse order.)

Mike Hillberg, an Architect who has made major contributions to Xaml, is blogging @ msdn.  Here are Mike's posts about Xaml.

Rob Relyea - There's Something About XAML - Published July 2006

Posts on Xaml from rrelyea.spaces.live.com