What's your favorite RoR editor/IDE?

I'm very happy with Ruby in Steel (http://www.sapphiresteel.com/). The
Intellisense code completion and the proper debugger really set this
one apart. The basic version is free but you will need a copy of
Visual Studio. (And if you're on a Mac, like me, you need to use a VM
as well)

I also use Ruby in Steel and I am extremely happy. Ruby in Steel is
excellent for development on a Windows platform. I agree with Fjan,
the debugger is brilliant. It is very easy to add a breakpoint and
inspect variable values. The developers of Ruby in Steel are also
very helpful, knowledgeable and accessible. Ruby in Steel really makes
me a more productive Rails developer.