A quick list, to be expanded. Did I miss something?

• The Rails Ways, Obie Fernandez — currently the absolute best reference to have around
• Programming Ruby, Dave Thomas (a.k.a. “The Pickaxe”) — maybe there should be one around in your company, but I don’t think it’s the best for experienced developers
• Ruby Cookbook, Lucas Carlson & Leonard Richardson — much better suited for programmers who are proficient in other languages and just want to know how to do the same things in Ruby style
• The Ruby Way, Hal Fulton — highly recommended, very complete
• Ruby for Rails, David A. Black — shows how Ruby is leveraged to create the smooth development experience one has with Rails
• Rails Cookbook, Rob Orsini — maybe better wait for the next edition

• Rails Recipes — dto, maybe better wait for the next edition

• railscasts.com — quick video explorations of lots of features you always wondered about

• http://www.infoq.com/ruby/ — the best news source :-)
• http://www.rubyinside.com/ — a good news source
• http://www.loudthinking.com/ David Heinemeier Hansson’s blog
• http://weblog.rubyonrails.org/ — the official weblog of the Rails team
• http://headius.blogspot.com/ — Blog on JRuby by its lead dev
• http://peepcode.com/ — Screen casts and books