Phil Spector has written an excellent introduction to R in his book Data Manipulation with R.  I recommend this book because it has a lot of short to-the-point examples, isn't cluttered with object-oriented theory or graphics.  Mr. Spector's book is focused mainly on data manipulation whereas other R tomes tend to add in graphics and statistics which can be overwhelming to an R beginner.  A nice addition to this book are the chapters on how to interact with databases from within R.  This book is worth the price and should be on your desk!  To order this book from Amazon, click this link: Data Manipulation with R (Use R).