I use RadRails, and yes, you can add other cool Eclipse plugins. But to add a cool plugin, you have to add not only the plugin itself but all plugins on which it depends. I've successfully added WickedShell to RadRails, but to do this I also had to swipe org.eclipse.pde and org.eclipse.jdt from a standard Eclipse installation, and add these plugins to the RadRails plugins directory.

> RadRails (www.radrails.org) if you plain on doing any Rails 
> programming.
> RadRails is based on Eclipse, RDT and custom develpment.
> (doesn't have HTML code complete, code complete from classes are hit 
> and miss,
> doesn't really allow you to add other cool Eclipse plugins :(   )