I went looking for the current state of IDE's for Ruby and in particular Ruby on Rails. In fact even more specifically for jRuby since I am not very interested in Ruby or ROR unless it is hosted on the JVM.
I found RadRails and RDT. Both of these are based on the Eclipse IDE platform. The former apparently based on the later. I installed and attempted to use both with jRuby. I had little success in this effort and from what I can gather jRuby support is yet to come for these packages.
I grabbed one of the Netbeans 6 nightly builds and was presently surprised to find jRuby there. A little more searching reveled this site which has done a far further exhaustive review of various Ruby IDE's than I have seen so far. Tor Norbye's blog section on Ruby also provides news straight from the source on this effort.