I have pretty specific requirements for an Eclipse IDE. Firstly it needs to support Java, along with Ant, Tomcat, and JUnit by default. Secondly, it needs to support PHP5, which is what I do most of my web development in. I also use Subversion as my source control system, so an interface to that is required. Finally, it needs to support Ruby as I write all of my test and utility scripts in that language.
The difficulty is that as my requirements are diverse, it is hard to get an "all-in-one" build that has all of these features in place, so I end up spending ages installing separate Eclipse plugins from different providers which is painful.
To avoid this pain, Yoxos have a nice online system that allows you to define your specific set of Eclipse plugins, then download your bespoke all-in-one build in a single click:
Yoxos OnDemand - EclipseSource - http://eclipsesource.com/en/yoxos/yoxos-ondemand/
Updated 2021 : note that the above post was originally published in 2009, but is left here for archival purposes. It seems that Yoxos OnDemand service is no longer active, so I have unlinked it above.