<p>Elementree has become the accepted standard for interacting with xml.  What is the prevalent web service/SOAP library in use today?</p>

I'm not sure about an accepted standard, but I've found
SOAPpy
to be fairly straight-forward and useful library for handling SOAP-based web services.
SOAPy is a SOAP/XML Schema Library for Python. Given either a WSDL or SDL document, SOAPy discovers the published API for a web service and exposes it to Python applications as transparently as possible.
IBM provide a
good walk-through and example
on their site for getting started with SOAPpy.
SOAPpy's no longer under active development, but is instead being folded into Zolera SOAP Infrastructure (ZSI) at the
Python Web Services Project
. This project however has alos
not seen much activity
since November last year.