Just need help on what book to buy for ruby

I subscribe to Safari on oreilly.com, which lets you have 10
electronic books at one time for $9.95 / month. You can switch books
out after you've had them for awhile. What's good about that is that
after you've learned something, you can switch those books out for
something new you're learning.

I found the $9.95 option hard to find when I signed up -- they really
want you to do the $19.95 / month option. 10 books has been enough
for me though.