IntelliJ has it's own GUI Builder:
http://www.jetbrains.com/idea/features/gui_builder.html
But there are also 3rd party plug-ins.
The best so far that can work standalone or as a plug-in for IntelliJ, Eclipse, Netbeans etc. is JFormDesigner: http://www.formdev.com/
JFormDesigner is the best UI Designer I've tried so far: just take a look at the demos.
