Is it possible to create a good GUI for Mac OS X applications written in Java?

You can create a Java-Cocoa application, and use Interface Builder to hook standard Cocoa interface elements to Java code. This unfortunately means that you'll have to have a separate build for OS X and other platforms, but if you keep your GUI code firmly separated from your application logic (and don't make frequent changes to the GUI), this can be an acceptable tradeoff. (This assumes that you don't want to use any Cocoa in your application logic, so no Core Data etc.) The reason that Java applications so frequently have ugly interfaces in OS X is that they're using the standard Java UI components which have been skinned to resemble Aqua components. They don't quite have the same default behavior as interfaces built with Interface Builder (for one thing, you use Java layout managers rather than the native approach) but it is possible to improve things, see [1]. "Bringing your Java application to Mac OS X.", http://java.sun.com/developer/technicalArticles/JavaLP/JavaToMac/

OS X these days has support for Java 5, which means that you can use Java FX: http://javafx.com/ Alternatively, Java does integrate well with Adobe Flex. Both of the above make it much easier to create an attractive GUI. However, if your aim is to achieve a truly native look and feel, Java-Cocoa is possibly your best bet, although it does drag you away from the write-once-run-anywhere ideal.

A good GUI or a mac native feeling GUI? PHPStorm, Eclipse and many other Java programs have great GUIs built using Swing.  But they won't have a mac specific look and feel.  Thats kind of the point of cross platform GUIs.

take a look at the Quaqua look-and-feel for Swing : http://www.randelshofer.ch/quaqua/