You have severel options
- FEST - compatible with TestNG and JUnit, framework is written to be use specially for Swing testing so it's very fast, in can take screenshots after failures, even sometimes determine the cause of this failure and other features. I would defintely give this one a tyr
- Marathon - looks very cool too, also has handful of features but unfortunately has a paid license
- Sikuli - image-based testing framework, allows you to write test scripts in Java
- Cucumber - you can write your tests in plain English, looks very interesting, so I would definitely give this one a shot
- and others...
As you can see, there are many frameworks, so the best is probably to go through their examples and basic tutorials and just grab what fits you the most.