Why's (Poignant) Guide to Ruby: http://poignantguide.net/

This is good for your first steps. Then check out The Ruby Way to dig in deeper:

http://www.amazon.com/Ruby-Way-Second-Addison-Wesley-Profess...

I'm quite fond of http://www.amazon.com/Ruby-Way-Second-Addison-Wesley-Profess... while there are some people who love the pickaxe book (first edition is free on http://www.ruby-doc.org/docs/ProgrammingRuby)..and others.

As for free guides, I love pointing people to http://poignantguide.net/ruby/