DeveloperWorks : An introduction to XML. Build a dynamic organization tree using GWT and RESTful Web services.
JavaScript. Tip: The zen of XSLT. Ten years ago, when XSLT was relatively new, I struggled to understand it.
It was too difficult to use and too challenging to debug. After I came to understand the strengths and weaknesses of XSLT and—more importantly—its paradigm and how and when to use it, however, XSLT is now a favorite tool that's a pleasure to use. XSLT is elegant and extremely powerful when applied well to a task for which it is suited. Have you ever used a hammer and screwdriver to loosen a nut from a bolt? You place the screwdriver blade on one side of the hex nut and tap the screwdriver's handle with the hammer.
Python. Regexp.