Check out ThunderBird: A Sample DITA Documentation Set to Play With by ditawriter. Here is an excerpt:
Here’s something I think needs to be more widely known: sample DITA files mimicking a professional manual set for a fictitious product called Thunderbird. I’ve been using this example code for a couple of years now in demos and for presentations, and there’s at least one person in every audience…
The full article is available here.