Once you've grasped the basics of creating web applications with Rails and are looking for further reading, I highly recommend you check out both the RSpec Book and The Well-Grounded Rubyist.
The former gives a great overview of behaviour-driven development with an eye to Rails, and is worth reading because the Ruby community has a strong emphasis on testing and most people are using the tools described in the RSpec book.
The latter is the best book out there for getting into a Ruby mindset and developing your knowledge of the language from 'the pretty guts behind Rails' to understanding both the guts and the ethos of the language, which approaches many things with a very different perspective from C# and similar languages.