ElementTree and lxml:

Start here if you want to write new code for XML processing

ElementTree tutorial: http://effbot.org/zone/element.htm

lxml tutorial: http://lxml.de/tutorial.html

Python XML Processing with lxml: http://www.nmt.edu/tcc/help/pubs/pylxml

Dive into Python 3, chapter on XML processing: http://diveintopython3.ep.io/xml.html

DOM/SAX:

Start here if you need to maintain existing DOM/SAX code that uses the xml.dom and xml.sax packages, or want to process XML using these packages

Note: some of these also describe the use of PyXML, which is an outdated XML package that is no longer maintained and should not be used in new code.

Python XML FAQ: http://www.rexx.com/~dkuhlman/pyxmlfaq.html

Introduction to different XML libraries: http://diveintopython.org/xml_processing/index.html