I wasn't sure whether to post this in client side, server side, beginners, or web site design, but here goes....
If you are running a course in XML, proably the teacher is best at this kind of stuff. I've got "Beginning XML" by Wrox, and it's an ok book, but it seems that some programming knowledge really helps for this book. A good book I've heard is the Visual Quickstart to XML, giving good concepts behind the knowledge...so, I'd probably reccomend this, although I haven't read it.
The Visual Quickstart book is good, but to cover nearly every aspect of XML, the 1000-page XML Bible is hard to beat. It's very well written and comes with a great CD-ROM. I have very little programming experience, and I'm picking up XML very quickly with this book.
XML Bible has tons of examples, maybe a little too many. And as for real-world apps, unless you have to keep track of baseball stats or make a family tree, not really. I got this book free with my XML class (well, I'm sure it was added into the tuition somewhere), and I like it because of its extensive coverage of XSLT (80 pages just for that) and clear explanation of namespaces.