What are some good free resources for learning Ruby?

There too many to list here, so here are a few of the best known ones:

• Humble Little Ruby Book provides a great overview of the language, from installation to the standard library. Available for free in PDF and HTML form, or can be bought as a paperback.
• Ruby Koans are a set of programs design to teach Ruby with a test driven philosophy.
• Hackety Hack is a program designed to teach the basics of programming. It's best suited for those with no to little to no previous programming experience.
• Programming Ruby (The Pickaxe book) is the first and best know Ruby book. The first edition is free online, but many consider it to be dated.
• _Why’s (Poignant) Guide to Ruby is probably one of the only programming books with comic strip intermissions. It's unique style doesn't appeal to everyone, but most will agree it's a lot of fun.