There are two that you can use (I've used them both, and they are both very powerful, and easy to use):
- NetBeans which has a built in GUI Builder.
Or you can use:
- Eclipse with the Windowbuilder plugin
- (it can be downloaded here and here)
Personally, I prefer Eclipse with Windowbuilder, but that's just me. You can use either one.
Here is a picture of the Windowbuilder plugin:
And here is a picture of NetBeans' built in GUI Builder: