XSL and XPath are very powerfull tools when working in the web (or do data conversion). Here are some snippets I found extremely helpful over the time.
Take a xml with loads items, and you want to display it - 4 in a row - in a table. This neat snippet does exactly that.
Search Replace Functionality with XSL 1.0
It happened already quite often, that I had to "misuse" a field ina xml-based cms solution. For example I created a comma seperated list in order to have all information available in xsl. This snippet shows you how to take such a list and play with it as if it were a subtree - in xslt 1.0.