Rails Up and Running - it's only for Rails version 2 but this was for me the most effective book for learning rails. They should really reissue the book for version 3. I bought it 4 months before rails 3 was released but I still refer back to it for some stuff. It doesn't make a lot of sense now but since I was just starting Rails had some exposure to 2 and 3 it was very helpful - http://shop.oreilly.com/product/9780596522018.do
Getting Real - Its free so no excuse not to download it http://gettingreal.37signals.com/
Start Small Stay Small by Rob Walling - http://www.startupbook.net/
The Rails 3 Way by Obie Fernandez - This has been huge benefit to understanding rails more than any other online tutorial or documentation - http://www.informit.com/store/rails-3-way-9780321601667
Rails Up and Running - it's only for Rails version 2 but this was for me the most effective book for learning rails. They should really reissue the book for version 3. I bought it 4 months before rails 3 was released but I still refer back to it for some stuff. It doesn't make a lot of sense now but since I was just starting Rails had some exposure to 2 and 3 it was very helpful - http://shop.oreilly.com/product/9780596522018.do