J2EE Web Services by RMH is probably the best book to date on Java Web Services. Some of the standards are currently being superceded, but it's still very relevant.
If you want a quick read, and a fast overview Java Web Services from O'Reilly explains most of the theory on
SOAP, WSDL, UDDI, JAXR, JAXM, JAX-RPC and some other good topics. Not the best book if you're looking for a lot of sample code though...
SCJP 1.4, SCWCD J2EE 1.4, SCJD J2SE 1.5, SCBCD J2EE 1.3, SCDJWS (In Progress)