The Adobe Photoshop Lightroom Book by Martin Evening
I got Lightroom along with CS3 a few months ago and was looking for a good book on it. I got both Evening's book and Kelby's. I have found Evening's book head and shoulders over Kelby's typical recipe book.
Evening was one of the Lightroom developers and you get under the hood as to what all it can do and why. He presents an interesting work flow and show how you can go back and forth from Lightroom to CS3 and back to Lightroom for the tools it doesn't have.
If you are going to start with Lightroom, this is a need reference and guide to Lightroom work flow.
Get it, you'll wonder how you did without it.