Packt Publishing has released a new edition of MODX Web Development – Second Edition. Though I rarely use MODX these days, I do still consider it a valuable and quality CMS. Clients have found it pretty intuitive, especially for basic edits and updates.
If you’re interested in getting started with or just learning about MODX, I do recommend this book. It covers MODX Evolution, not Revolution. Personally, I still prefer Evolution over Revolution; it just seems to jive better to me, since I haven’t spent too much time with Revolution.