Try NetBeans 6.1 Beta it rocks.
Here is Netbeans forum on Nabble
I have Netbeans 6.1 beta installed on both Ubuntu 7.1 and Fedora 5. It
runs very well. I run Nebeans on Windows as well, so it is very
convenient. I don’t have a Mac so I cannot comment on it.
For light-weight editing, both VIM (or GVIM or Cream with Ruby plug-in)
or gedit which comes with every linux installation are good enough.
So really with NetBeans IDE and these two editors, I don’t have a need
to look elsewhere. I have been a long time Eclipse user and still use
Eclipse for Java work, but NetBeans is way ahead of anything open-source
in the Eclipse world for Ruby and Ruby on Rails which is my primary
interest at this point.
Hope this helps.