There is worthwhile stuff in all of the current Puppet Books, depending on how you use Puppet and what level of experience your at. Pro Puppet (2nd edition mentioned above) seems to be the bible and is the one I keep referring back to, but the best book I have looked at so far is probably Extending Puppet. Here is a recommended reading order and my casual opinion:
Puppet 3 Beginners Guide: John Arundel
- Well written and great content but the formatting is a bit annoying, particularly if your on an e-reader. Great introduction to Open Source Puppet.
Puppet 3 Cookbook: John Arundel
- The cookbook style works really well for Puppet, this book has a lot of practical examples, key concepts and best
Puppet Types and Providers: Dan Bode and Nan Liu
- Dev oriented but essential
Pro Puppet (2nd edition)
- Dense and authoritative, the 'if you only buy one puppet book' book
Extending Puppet - Alessandro Franceschi
- Would consider this the 'best' puppet book currently available, not for beginners
Mastering Puppet - Thomas Uphill
- Not for beginners, lots of wow factor and pushing puppets capabilities.
Haven't read Puppet Reporting yet but its supposed to be good, and the book on MCollective also good on first impression.