Two examples would be Google, and the microsoft Terraserver, which both have publicly advertised web service interfaces.
SOAP once stood for "simple object access protocol". The bad news is that the "S stands for simple" has become a bad joke and the name officially now just stands on its own. SOAP is one of the underpinnings of the Microsoft .NET scheme, and you get to learn about XML, WSDL, and many other things, if you want to really understand the protocol.
A sensible plan would be to just use one of the many SOAP packages that have
been written for perl, python, ruby, tcl, or whatever language you like.
On my fedora core 7 system, I already have soap as part of ruby, as well
as tclsoap. Perl has both SOAP and SOAP::Lite (but neither are on my system).
SOAP and Java have some kind of relationship.
I can get a couple other soap packages via:
yum install SOAPpy yum install php-soap
SOAP links:
Uncle Tom's Computer Info / tom@mmto.org