Delynn Berry has developed a useful plugin called UserStamp. Whereas Rails has built in support for automatic columns such as created_at and updated_at, it doesn't (quite rightly) support concepts such as created_by, as these belong in the application domain. It's a commonly required feature though, and Delynn has done a great job of packaging it up.
Pat Eyler of O'Reilly's Ruby blog has interviewed James Gray of Ruby Quiz fame. James talks about how he was won over to Ruby via Perl 6, and how the Ruby Quiz has continued to explode in popularity.
Stefan Kaes takes a look at common performance problems with Ruby on Rails. He looks at:
From the ever-productive Erik Veenstra comes AllInOneRuby, a "Just-in-Time and Temporary Installation of Ruby". The concept is simple:
Rather than use the send_file or send_data methods to send an entire, completed bulk of information back to the client, David N. Welton wanted to, effectively, print stuff to the client bit by bit. He worked out how to do it and presents his findings and sample code here.
Chris Anderson looks at deploying Rails apps with Capistrano and Mongrel on Planet Argon. He provides a whole pile of recipe snippets, as well as some Capistrano recipes for Mongrel 'spinner' and 'restart' tasks.
Inspired by the legendary (amongst Perl programmers anyway!) Perl Cookbook, comes the Ruby Cookbook. It has the equivalent examples from the Perl Cookbook but in Ruby form, of course. The basic sections are mostly complete, although some of the later sections are barely covered yet. Still, if you want to see the basic recipes for dealing with strings, numbers, dates and times, arrays, hashes, file I/O, process management, and so on, it's a cute little resource.
This cool Ruby cheat sheet quickly runs you through.. reserved words, syntax rules, escape characters, regular expression characters and formats, file mode strings, special variables, expressions, operations, built in classes, and more. Extremely useful to beginners and advanced Rubyists alike.
Pagination in Rails is good, but it can lack flexibility in many situations. At that point it's time to roll your own. However, Phil Bogle and Laurel Fan came up with a solution they call paginate_by_sql that can solve some of the custom pagination problems. This needs to become a plugin.