3 links
Gentle Introduction To SOAP
intertwingly.net
This document provides an introduction to the SOAP protocol. Only a basic knowledge of what a procedure call is and some familiarity with XML is required.
Real SOAP Security
msdn.microsoft.com
Article by Matt Powell on MSDN. Despite the fact that SOAP as we know it today has no real support for security, there are secure XML Web Services in existence today.
Using WSDL in SOAP Applications
-106.ibm.com
Provides an overview of WSDL, history and background of various related technologies such as SOAP, and UDDI. By Uche Ogbuji, Fourthought, Inc.