Chris Anderson's new book, Free, is actually subtitled, "The Future of a Radical Price," but he does a great job of explaining the economic concepts related to Free. And he does not sound like a dry economics textbook while he's doing it (at least not to me).
The Free concept at its best is shown by Google, which gives away search but learned to sell ads alongside the search results. This is a very old concept, actually. Radio, and then television, gave away content but sold ads. Some of the new tools, such as YouTube and Twitter, have mastered the free part, but are still struggling with the pay part.
Here are a few of the gems from this book:
If I ever go back to teaching, I'll use Free to teach about complementary goods, in about chapter 3.
I recommend this book highly. For listeners, there's a free abridged audio file available here.