I had a wonderful time at Tampa Day of Ruby this past weekend where I received an overview of the Ruby Language, Ruby on Rails, Cucumber, RSpec, and development on the Mac in general. For more info see: ASP.NET MVC and Ruby on Rails This Past Weekend.
This was truly an interesting experience and while most people were using Vim, and TextMate to do their development, I downloaded JetBrains RubyMine, which is a brand new IDE specifically for doing Rails Development.
As a newbie, I can't really tell you how good it is at this moment given my lack of real knowledge on Rails, but I can say that it truly helped me during the class as I could easily navigate across the project, edit code with code completion and syntax highlighting, etc.

Some of the JetBrains RubyMine 1.0 Features include:
- Intelligent Editor: code completion, code snippets and automatic refactorings
- Project Navigation: wide range of views and one-click jumping between components
- Error-Free Coding: on-the-fly code analysis and type inference
- Web Development with Ruby on Rails (including best-of-breed HTML, CSS and JavaScript editing support)
- RSpec and Test::Unit support, with GUI-based test runner
- Ruby Debugger: full support for Rails applications debugging and easy-to-use interface
- VCS Integrations: Git, Perforce, Subversion and CVS with changelists and merge
- Open API and Plugin Development SDK, ensuring IDE extensibility and flexibility
If you are a new Rails Developer like myself or a seasoned expert, I highly recommend checking out JetBrains RubyMine.