There are gui editors for Netbeans and Eclipse (as a plugin). Both are free
and opensource.

I provide Forms, a no-charge open source layout system.
Forms helps you build elegant Swing panels quickly,
it makes simple things easy and the hard stuff possible,
the good design easy and the bad difficult.

Forms can do several things that other layout managers
or layout systems, or visual designers can't do. Anyway,
the project's primary goal is to reduce the costs and time
necessary to lay out and implement multi-platform design.

There are a bunch of GUI builder projects that are in
the process of adding support for the JGoodies Forms.
AFAIK, none of these projects is ready to be shipped.
However, I'd recommend to give hand-coding a (last) try.
If you have paper for the design drafts and an IDE that
offers hot code swap you can work quite well with the
Forms even without a visual builder.

The JGoodies Forms Demo utilizes the Forms and shows
a bunch of layout tasks that you cannot implement with
the GridBagLayout, or TableLayout - although these are
essential for screen design.

Hope this helps,
Karsten Lentzsch
JGoodies :: Java User Interface Design

Project home - https://forms.dev.java.net/

Downloads - https://forms.dev.java.net/ProjectDocumentList

Forms Demo -
https://forms.dev.java.net/servlets/ProjectDocumentList?folderID=621

Articles & Presentations - http://www.jgoodies.com/articles/