The question of which book to use to get started in iOS development keeps coming up in the in the SAiOS community.
The problem beginning developers face is that many publications are out of date. Given that Xcode 4 was released in March of this year and iOS 5 just a few months ago in October, it's not surprising.
So, as of this post date, here's a few books you can use to get started with the current platform and tools.
Begininning iOS 5 Development by David Mark, Jacking Nutting, and Jeff Lamarche
Many developers have started on what is coollequially reffered to as the Grapefruit Book. It provides ample walkthroughs exposing much of the iOS framework with the beginner in mind.
Cocoa Programming for Mac OS X (4th Edition) By Aaron Hillegass and Adam Preble
Objective-C Programming: The Big Nerd Ranch Guide By Aaron Hillegass
While not technically an iOS development book, Cocoa Programming for Mac OS X has served as a touchpoint for many developers on their journey to iOS development. While Big Nerd Ranch does have an iOS development book, the update won't be available till March.
iOS SDK Development by Bill Dudney and Chris Adamson
This book is only available in ebook beta form, but you can't go wrong with the veteran pair of Bill Dudney and Chris Adamson. You may recognize Dudney as an Apple Developer Evangelist.
I don't know much about the follwoing titles themselves, but these turned up in my research. The publishers are reputable and may be worth a read.
Learning iOS Programming: From Xcode to App Store By Alasdair Allan
Objective-C Fundamentals By Christopher K. Fairbairn, Johannes Fahrenkrug, and Collin Ruffenach