Recommended Reading

Specifications

SOAP Version 1.1 Remember that SOAP1.1 is not an official W3C standard.
SOAP Version 1.2 Part 0: Primer This and the follow-on sections cover what the W3C think SOAP is and how it should be used.
Web Services Description Language (WSDL) 1.1
RFC 2616: Hypertext Transfer Protocol -- HTTP/1.1
JAX-RPC Specification 1.0 The public API for Web Services in Java.
XML Schema Part 0: Primer The W3C XML Schema, (WXS) is one of the two sets of datatype SOAP supports, the other being the SOAP Section 5 datatypes that predate WXS. Complicated as it is, it is useful to have a vague understanding of this specification.

A Gentle Introduction to SOAP
A Busy Developer's Guide to WSDL 1.1
To infinity and beyond - the quest for SOAP interoperability
Java develoment with Ant (chapter 15)
When Web Services Go Bad
JavaOne 2002,Web Services Today and Tomorrow (Java Developer connection login required)
The Java Web Services Tutorial: Java API for XML-based RPC This is part of Sun's guide to their Java Web Services Developer Pack. The examples are all based on their JWSDP, but as Axis also implements JAX-RPC, they may all port to Axis.
Using Web Services Effectively. Blissfully ignoring issues such as versioning, robustness and security and all the other details a production Web Service needs, instead pushing EJB as the only way to process requests, this is Sun's guide to using web services in Java. It also assumes Java is at both ends, so manages to skirt round the interop problem.