Like others have mentioned, NetBeans' visual editor is pretty good, but it's based pretty heavily on the Swing Application Framework, so you'd need to get an understanding of how it works to properly use it (although you don't need to dig in to just test things).
Other than that there are also:
- the IntelliJ IDEA visual editor (flash demo of the features)
- and Eclipse's Visual Editor
Personally I've used NetBeans' and IDEA's visual editors. Both are nice, but I thought NetBeans had a leg up, because it doesn't use any proprietary way of saving the GUI structure and instead does something similar to what Visual Studio does - auto-generating the code that you can then add to. IDEA stores the information in a separate file which means you have to use IDEA to edit the layout visually later.
I have not used Eclipse's Visual Editor.
My vote is for NetBeans' visual editor. I think it satisfies what most people are looking for in a visual editor and leaves it flexible enough to plug the holes manually through code without affecting the visual editor (so you can switch back and forth between code and design views without breaking either).
