Java has Eclipse, .Net has Visual Studio (with ReSharper) and now Ruby has NetBeans! The NetBeans IDE is fast becoming the IDE of choice when it comes to Ruby development. It supports auto-completion, smart navigation and refactoring. In addition to this, NetBeans supports Ruby on Rails!
There are numerous ways to get up and running. In a previous post I suggested Instant Rails as a quick start. You can use NetBeans and Instant Rails together; Brian Leonard’s Blog explains how to do this. If you download the Ruby bundle of NetBeans you can skip some of the steps in Brian Leonard’s tutorial.