I was looking for ways to improve the look and feel of Java applications - for presenting my Java-based research work as a nice-looking app and for demos. I was inspired by some of the Adobe AIR themes out there, and I found some interesting stuff.
Among the many Swing Pluggable Look-and-Feel solutions is one that really stands out - Substance. It looks absolutely phenomenal, with a variety of options and customizations, plus its open-source. It easily stands out as a must-use PLAF for Swing. Take a look at some Substance screenshots.
There's that for themes ... but how about fade effects and transitions?
A little bit more searching reveals the animation layer, which includes transitions - in fact, automated transitions with no changes to app code! You need to see the above link for yourself to believe it.
Apparently, this fade animations is part of the laf-widget project now.