We'll be adding more here when we get around to organising the web site properly but for now you can find some links to useful Ruby and Ruby on Rails books.
Dave Thomas, Chad Fowler, and Andy Hunt (Paperback - 22 Oct 2004)
David Black (Paperback - 30 Jun 2006)
Dave Thomas, David Heinemeier Hansson, and Leon Breedt (Paperback - 15 Jun 2005)
Chad Fowler (Paperback - 23 Jun 2006)
Bruce A. Tate and Curt Hibbs (Paperback - 5 Sep 2006)