JetBrains have just released the first beta of their IntelliJ IDEA Ruby Plugin. I've been using builds from the source repository for a while, and its my favourite environment for building Ruby on Rails applications. The strange thing is, I don't use it because I think it makes IntelliJ a great Ruby environment. I use it because IntelliJ is already a great environment for building HTML and CSS. When I'm building Rails apps, the framework allows my code to be so lean that I actually find myself spending more time working on the presentation of the system.
IntelliJ has been a great environment for HTML and CSS for years now. Its certainly very familiar to me from my Java web app development experience. The release of this plugin makes it at least an adequate environment for Ruby development. If history is anything to go by, JetBrains may well turn it into something which makes me wish I was forced to write more Ruby code in a Rails app :-)