RubyMine 1.0 – A Solid, IntelliJ Based Ruby on Rails IDE ($49)

RubyMine offers all of the features you’d expect from a high-end IDE:
* Code completion
* Code snippet support
* Refactoring tools
* Project file management / navigation
* HTML, CSS, and JavaScript editing (including Erb support)
* RSpec and Test::Unit support (with GUI-based test runner)
* Built-in Rails console
* Ruby debugger (with full support for Rails apps)
(via rubyinside.com)
(Link: RubyMine 1.0 – A Solid, IntelliJ Based Ruby on Rails IDE ($49))