I love this slide from Gary McGraw at Cigital.
Web Services Security BookSample chapter (PDF download)Read the forward by Patrick Gannon, CEO of OASIS
Included in the following Amazon.com "Listmania" lists : Great books on Web Services", "Must read technology books"
Hardening Network Security book - read the XML security chapter here
More writings on XML and Security (XML Journal, Web Services Journal, Enterprise Architect Magazine, Java Pro, ...)