This San Mateo development company makes a freely downloadable convenient packaging of many plugins for Eclipse called Aptana. I was recently in an environment where Aptana came pre-installed. Not only is it a good IDE for RoR, it also does a somewhat decent job (sans debugging) for PHP, Python, HTML, CSS, and Javascript. According to their own web site, their IDE also supports Adobe Air and the iPhone.
If you are currently using Eclipse, then do you also use Aptana too? What, if any, are the drawbacks to using Aptana?