I know there are a lot of threads about books, but some of them are as
old as 2006 - and I think it would be nice to get a more up to date list
of hot Ruby books, especially for anyone interested in learning the
latest version of Ruby, 1.9 (it's still ok to recommend older books if
you feel they are still relevant).
Makes sense

.
I for one will be very eager to see which of the books you have read you
have 'fallen in love with' - they're the ones I will most likely get
first
I have read, and absolutely love "The Ruby Programming Language" by
Flannagan and Matz, and "Ruby Best Practices" by Gregory Brown. While
the former serves as a fantastic reference, the later deals with Ruby
programming practices in real projects and picking up a lot or Ruby
idioms.
Another interesting book that I had a chance to lay my hands on was
"Practical Ruby Projects" by Topher Cyll. I found it more fun than
practical; even the author sub-titles it "ideas for the eclectic
programmer". It deals with things like: generating SVG animations,
implementing Lisp in Ruby (loved this chapter), creating music with
MIDI, Mac OS X GUI, Genetic Algorithms. Would suggest reading it in
leisure time, or at an intermediate level.
Hal Fulton's "The Ruby Way" is another book that I have read. It was
the first Ruby book that I bought as The Pickaxe was way expensive in
India back then. I was able to learn a good deal from it as a
beginner. I would not recommend it though (not even to a beginner) as
you can learn the same thing (without paying for the book) from the
Ruby documentation, or Google. For the same reasons, I think it has
lost much of its significance now.
I have done some light reading on "Enterprise Integration with Ruby",
and "Practical Ruby for System Administration". They contain some
decent examples, but have a very beginner-ish and closed feeling to
it. I don't think that they don't teach you anything concrete, rather
gives you the answer to some closed form problems that you could have
come up with (think, google, think, implement) with any way.
Some books that have got good reviews, and I am looking forward to
read (waiting for cheaper Indian reprint to come out

) are "Design
Patterns in Ruby", and "Refactoring - Ruby Edition". I think these
books are relevant as they teach you something concrete - patterns,
styles, and practices that you can apply, and reapply to different
problems later. Would refrain from commenting more as I have not
actually read them.
tl;dr - Learn Ruby by reading "The Ruby Programming Language" while
get better at it by writing, and reading a lot of code (FOSS, fun
projects, rewriting class room assignments in Ruby). And yeah, "Ruby
Best Practices is excellent, and free (I love advertising it

).