If you are using Visual Studio 2005, you may like to keep an eye on our IDE, Ruby In Steel. The first public beta has only just been released so it is far from 'feature complete'. It currently has colour coding, code collapsing, an integrated docked console and syntax error location. The next beta will introduce simple debugging. Over the next few months we'll add more powerful debugging, IntelliSense etc. The project is based here:
http://www.sapphiresteel.com
best wishes
Huw