Core Animation: Simplified Animation Techniques for Mac and iPhone Development
Authors: Marcus Zarra and Matt Long
http://www.informit.com/store/product.aspx?isbn=0321617754
For a while, Bill Dudney's Core Animation for Mac OS X and the iPhone was the only non-Apple reference text on Core Animation. While his book and this new book by Marcus Zarra and Matt Long are both great references for the topic, if you have to pick just one I'd recommend this one. This book benefits from having been written and released over a year after Bill Dudney's book, and it goes into more detail than he does.
This is a gorgeous book, with a lot of full-color illustrations of animations and great typesetting. The content covers both beginning and advanced topics on Mac and iPhone, with a significant amount of text devoted to iPhone-specific issues.
If you have any interest in the topic, I highly recommend you grab this book.