I've recently been using JSEclipse , the Eclipse plugin from the InterAKT folks and much prefer it over the WST components that the Eclipse project provided so far. Now I finally got around to making the switch to the Aptana Web IDE and I think I like where this project seems to be heading. Check it out, if you haven't already!
Apparently based on the Eclipse code base and promised to be open source itself, Aptana is targeted mainly at Javascript development instead of Eclipse's Java core audience. With the open and flexible way in which it allows to integrate code auto-completion and API documentation of different Javascript libraries, it could well be an ideal IDE for Helma based development.
An interesting side project to come out of this effort is scriptdoc.org , which addresses shortcomings in the javadoc-style of documenting source code and API's, when used in Javascript environments such as Helma.
4.8.2006, 16:18Update: 8.9.2007, 11:22: Unfortunately, the Aptana project has changed from the Eclipse Public License to the Aptana Public License and Aptana is no longer open source .
Update 2: 23.9.2007, 10:09: The Aptana project has announced that due to the community reactions they intend to also license the APL code under the GPL .