I have the Graeme's Definitive Guide as well as the Grails Quick Start Guide from Pragmatic. I would opt for the latter if I was just starting out, only because I like the format and the book dives right into creating the TekDays application which was pretty fun to code.
Also, Scott Davis has some great Grails articles on developerworks that are worth checking out too.
"The Definitive Guide To Grails" (APress) by Graeme Rocher and Jeff Brown is the most comprehensive book on Grails that I've seen, but it's a reference book rather than a tutorial.
"Grails In Action" by Glen Smith and Peter Ledbrook (Manning) is an excellent and pretty thorough introduction to Grails based around a tutorial with lots of intelligent material on how and why things work a particular way. Plus their sense of humour is good fun.
Depending on your previous experience, I'd also recommend getting a good book on Groovy, because you'll find the language is extremely powerful if you start to appreciate the way it works, and especially the ways in which it is different from Java. Grails uses a lot of clever Grooviness, on top of lots of clever Spring stuff, and it helps to understand at least in principle how it all works.
My favourite Groovy book is "Groovy in Action" by Dirk Koenig (Manning), which will give you an excellent introduction to the clever things you can do with Groovy. There's supposed to be a new edition out soon (next year?), but the 2007 edition is fine.
Venkat Subramaniam's book "Programming Groovy" (Pragmatic Programmers) is also good, but doesn't cover as much as the Koenig book.
I am well seasoned Java developer. However, I have to get a good quality tutorial/guide through a complete practical example and hand holding to getting me grasp new stuff.
I have had heard very very good things about Grails and it's quickness and easiness in delivering of solution. After much trials, I found one documentation which was easy read and it worked first time. It took me about 3-4 hours to go through the book but by the time I finished, I felt good and confident to start a project knowing that I can solve/find solution for most what I will need.