Does anyone have any info on an IDE or editor that supports
auto-completion for Ruby?

So far I've been using Scite which came with the One-Click Windows Ruby
installer, but have not figured out how to turn on auto-completion (or
to be more specific, how to create the needed api file).

I just downloaded RDE, but the auto-completion seems half baked.  For
example, if I type the following:

a = [4,2,3]
b = a.

a pop-up is shown just like you would expect where I can select a
method of Array.  But then if I continue along to here:

a = [4,2,3]
b = a.sort
b.

.... no pop-up is shown -- it doesn't know that b is an Array.

Perhaps there isn't yet an IDE or editor for Ruby with auto-completion
features like those seen in Microsoft Visual Studio, Jet Brains IDEA,
or Eclipse?  If not, I would be interested in hearing what other
developers are using to create ruby code.

Thanks in advance,
 - Eli