The official documentation for the Rails framework. If you program like I do and just want a straight forward comphrensive reference - this is the closest thing available for Rails.
Just in case anyone hadn't seen this yet. If you are running rails 1.1.0 through 1.1.4, you're going to want to update to Rails 1.1.6 as soon as possible.
The Ruby language reference documentation. Great for programmers that like to refer to concise and (mostly) complete documentation while coding without flipping through a lot of prose.
The full text of the first edition of the most popular Ruby book around. It's a pretty good starting place for Ruby beginners (and a fair reference for seasoned Ruby programmers).
A great summary of the Ruby classes and their available methods. Smaller and quicker than using the RDoc if you just need info on a particular basic class (like hashes, strings, or arrays) and their methods.