RDT (Ruby Development Tool) seems to be the preferred plugin for adding Ruby support to Eclipse. However, I see that the main developer on that project has joined Aptana RadRails. Does this mean that project is no longer up-to-date for Ruby in Eclipse?
If so, which plugin is the preferred and best choice these days?
Try the Dynamic Languages Toolkit for Ruby. It's available from Eclipse's Software Updates panel.
Update May 2020: Ruby support was dropped in DLTK 6.0 in favour of Eclipse Solargraph.