My top book recommendation for Powershell 2.0 is, hands down, Windows PowerShell 2.0 Best Practices.

Any modern system administrator who wants to be efficient in his/her job should get into Powershell 2.0 - and this book will be a great companion on the way.

I promise you: It's a lot more fun to write an automated user creation script, than to e.g. manually create 30 users in Active Directory.
And once you have created that script - you can use it every time you need to create more users.
This book will assist you in writing powerful scripts like this to automate your daily activities.
It has got a lot of excelent real-world examples, together with simple explanation.

This book is the most in-depth book on the market about best practices regarding powershell 2.0. It covers subjects like remote scripting, Windows Management Instrumentation (WMI), and there is an entire chapter dedicated to ADSI (creating users, groups, computer accounts etc).

This book covers some of the basics, though it is not a beginners book. I recommend to have an understanding of Powershell, but if you have some scripting/programming experience, this book should still be easy to comprehend.

Read the reviews here to help make up your mind if you consider buying the book.

One last thing:
Make sure to get a hold of Windows PowerShell 2.0 Administrator's Pocket Consultant a must for any serious powershell scripter. it's a small, compact and cheap book that you can keep on your desk at all time for a brief overview of a subject when you need to look up details without need to go deeply into the subject.

The book has got on the spot, accurate, information on the most important areas of Powershell 2.0

If you want to learn Powershell from scratch I suggest you buy Windows PowerShell 2 For Dummies or Microsoft Windows PowerShell 2.0 Programming for the Absolute Beginner