I\'ve been coding basic UIs in Java manually and using NetBeans, but recently switched to Eclipse Indigo. I use the visual class builder to design SWT user interfaces in Ecl
You can also use Jigloo.
Their eclipse update site it, http://cloudgarden.com/update-site
I have used it in windows quite well. But when I use it in mac, most of the time it crash.
But windows builder seems better to me.
Since Google aquired Instantiations and then donated WindowBuilder to Eclipse foundation it is the preferred free, open source visual GUI editor for Swing, SWT and GWT.