If you’ve already got some programming experience under your belt and are searching for a book that’ll get you up to speed with Ruby very quickly, I strongly recommend Ruby by Example (written by Kevin Baird and published by No Starch Press, whose books on coding have impressed me).
As the book’s name implies, it covers the the Ruby programming language (with a little bit of Rails thrown in) through dozens of annotated examples, which covers not only the language but Ruby idioms as well. Experienced programmers will appreciate not being dragged through yet another set of introductory chapters (“this is branching…this is a loop…these are classes and objects…”). Any introductory material is saved for topics that might be new even to experienced programmers, such as chapter 6′s — Functionalism with Blocks and Procs — which may represent some of the best coverage of the topic in any Ruby book. (Even better, it’s available as a free sample chapter!)
Pair Ruby by Example with Agile Web Development with Rails (you could throw in Everyday Scripting with Ruby as a bonus) and you’ve got a killer combo for getting started with web development using Ruby.