I used JSF in Action, and found it OK. One problem is that it only covers JSF 1.1, and I am waiting for an update to cover 1.2.
Of all the books I have read, I found "JavaServer Faces: The Complete Reference" to be excellent, with one caution: oddly, it is a better tutorial than a reference. The index is awful, and it doesn't have reference material on the classes, only the tags and configuration files. However, the chapters actually do a better job of explaining what's going on behind the scenes than anything else I've read. Also, it covers JSF 1.2...in fact, it carefully points out what features are new to 1.2, so they don't get lost in the other information. It also has a chapter on Ajax components (which JSF in Action doesn't) and a good overview of Facelets and MyFaces.
I bought "Core JavaServer Faces", 2nd ed, c2007, David Geary and Cay Horstmann, Prentice Hall - covering version 1.2, with explanations on using 1.1. This is my first JSF book, I found it while browsing in a bookstore, I am very pleased with it. ISBN: 0-13-173886-0