SOAP

formerly known as the Simple Object Access Protocol

More than XML-RPC Even SOAP's RPC-oriented options are richer than those of XML-RPC, offering support for all XML Schema datatypes and a wider variety of options. SOAP's RPC feels more like objects than simple procedures.
More than RPC While RPC is definitely a key part of SOAP, SOAP's developers have separated the notion of RPC from SOAP itself, and SOAP envelopes can be used for nearly any kind of XML message.
Built on HTTP, but not bound to it While SOAP certainly started out using HTTP for its transport, SOAP is slowly separating from HTTP. Is SOAP on a different transport still "Web" Services? So far, it's still described that way.
WSIO Does it say anything that the latest Web Services vendor consortium is supposedly addressing issues of interoperability? (The W3C has also set up a few working groups beyond its existing SOAP work in the XML Protocol group.)