Here are two handy apps I use when I have to parse XML data.
firstobject XML Editor – This is a great tool that I primary use for formating XML into a more readable format. I just paste it in the editor, hit F8, and it beautifies it. It does more than that, but that’s what I use it the most.
Buba XPath builder – This is a nice tool where you can create an XPath search string and it shows you the results in real time by applying it to your XML data.