[jashkenas]

If Ruby intrigues you, there's no better place to start than with the Poignant Guide:

http://mislav.uniqpath.com/poignant-guide/

[techiferous]

TryRuby http://tryruby.org/ and Learn to Program http://pine.fm/LearnToProgram/ are better places to start.

The Poignant Guide is more entertaining but not the greatest for actually learning the language.