Disclaimer The opinions expressed herein are my own personal opinions and do not represent my employer's view in anyway.
Visual Xpath is a free Visual Studio addin that helps you test your XPATH statements against a source XML file.
One of my current projects is to use Microsoft SSIS to import a complex type XML file into SQL. As I only need certain types and data from the XML file, an XPATH query using the SSIS XML Task seems like a good idea. Trouble is I have to learn XPath. I'll add any good references I find to this post.
A good allround tool for XML work is http://www.stylusstudio.com