Well, I have two options: Objective-C on the Mac using Cocoa GUI framework, or Java for everything (Mac, Linux, MS-Windows) using the Swing API.
If you want to program in Objective-C targeting Mac OS X operating system for Apple Macintosh, iPhone, or iPod Touch - then the Interface Builder that comes bundled with the Xcode IDE (part of the Developer bundle) is really good.
You will need a Mac, of course, to be able to use it. If you have a Linux or Windows PC already, then you probably have a monitor, USB mouse, and USB keyboard. So you could get an Mac Mini for $599 and hook those up to it.
The Developer bundle is free. Just go to developer.apple.com and sign up for free Developer tools once you get your Mac.
If you are going to be a professional developer, then you might want to go there before you get your Macintosh and see if registering as a Pro and buying a Macintosh and stuff under that deal would net you more bang for your buck.
This Interface Builder of Apple's is pretty famous. It is what gave the NeXT computer is high reputation for being the way to create applications really fast. Wall Street financial firms, government agencies, and research types - plus a fair number of 3rd party commercial software developers - used it to create GUI applications very rapidly.
The name of Apple's Cocoa framework, by the way, used to be Next Step. When Apple bough NeXT from Steve Jobs, they renamed Next Step Cocoa. However, the classes still begin with NS as a little artifact of their heritage.
What people like about Interface Builder is that it has a very good layout manager and it lets you "wire" UI objects to other objects, making the latter "targets". Wiring them together this way creates a "connection".
So far this sounds very unexciting, I know. However, it gets exciting when you start doing it. You can design your actual runnable GUI in the designer and actually run it before you have written any code. Writing code lets you incrementally flesh out the user interface that have behavior more than UI stimulus-response behavior.
Anyway, the idea is that you can bang out a prototype extremely quickly, get feedback from someone based on this concrete GUI - and then fill in the details with Objective-C programming.
The most famous thing that was ever created with Next Step (Cocoa) is the World Wide Web (WWW). You may have heard of it. Well, the first web browser in the world was created by Tim Berniers-Lee at CERN in 1989 using Next Step, which had just come out the year before (1988).
He said he liked Next Step because it let him create his web browser very quickly. Even more impressively, his web browser not only allowed users to view web pages - his browsre also let users edit the web pages they viewed.
If you want to program in Java, NetBeans has a very nice Swing GUI designer.
It comes built into NetBeans. The GUI designer very easy to use and seems to have a full set of capabilities. My ownly dislike is that it puts commented sections in the code that you cannot edit. JBuilder did not put those annoying comments/restrictions in but JBuilder has pretty much faded from the scene these days.
Another downside of NetBeans is that it creates a .form file with the same name as the GUI class you are editing. Java code refactoring tools, other than NetBeans, are not going to know about this file. So, if you manually move the package the class is part of (or rename the class) - or use Eclipse or some other program to do it - you are going to have problems. You will need to be sure to use NetBeans to move/rename your class.
Eclipse had one in the form of an experimental plugin that was an okay start for a GUI designer called VE (Visual Editor) a number of years back. However, VE does not appear to have been updated in a couple of years.
I really like the true portability of Java programs. Java programs with GUIs are no exception.
I recommend adopting Java as your new language and using NetBeans as your first IDE, since you favor GUI program designs with a WYSIWYG editor.
Later, I suggest you also learn Eclipse. That way you will benefit from its more powerful code editing/refactoring capabilities.
You do not have to make an either-or choice between the two IDEs. With some caveats, like I have given - you can use both.