Rails-books.com reviews the most recent Ruby on Rails books.
For now, the site only lists books for the latest version of Rails (Rails 2), or books that have made available the changes needed for the examples to work on the latest Rails version, like RailsSpace.
Agile Web Development with Rails, Third Edition ($29.01)
Agile Web Development with Rails, guides you through the proccess of developing an online store with Ruby on Rails, explains Active Record, and goes through securing and deploying your RoR app.
The perfect book to get started with Rails 2, as most other books right now are aimed at older versions.
Ruby on Rails book | Ruby on Rails for Microsoft Developers ($31.49)
This definitive guide examines how to take advantage of the new Agile methodologies offered when using Ruby on Rails (RoR). You'll quickly grasp the RoR methodology by focusing on the RoR development from the point of view of the beginner- to intermediate-level Microsoft developer. Plus, you'll get a reliable roadmap for migrating your applications, skill set, and development processes to the newer, more agile programming platform that RoR offers.
Ruby on Rails book | Simply Rails 2 ($26.37)
Unlike other Rails books, this book doesn't assume that you are an experienced web developer, or that you've used Ruby before. An entire chapter is devoted to learning Ruby in a fun way, using the interactive Ruby console, so you can follow along at home. You'll be an accomplished Ruby programmer in no time!
The example application that the book builds - a user-generated news web site - is built upon with each following chapter, and concepts such as sessions, cookies and basic AJAX usage are gradually introduced. Different aspects of Rails, such as user authentication, session cookies, and automated testing are explored with each feature that is added to the application.