TanSanC

http://geeknizer.com/best-java-swing-look-and-feel-themes-professional-casual-top-10/

http://dock.javaforge.com/ 

The Look and Feel Libraries are broadly divided into two categories.

1. Skinnable
2. Non-Skinnable

Skinnable look and feel can’t only change the LAF of wigets in your application, but, can also change the look and feel of window title bars and borders. So here are few Professional and Casual themes that you can use to make your application much more attractive and vibrant:

Professional Themes

Nimbus

This is the theme that’s getting a lot of popularity, specially, after Solaris 10 adopted it.

Here’s how you can set it:

UIManager.setLookAndFeel("javax.swing.plaf.nimbus.NimbusLookAndFeel");

Here’s a screenshot:

Substance
Substance has 6 different flavours for the metallic Look an Feel. The Good one is below. You can checkout other color schemes here (though they are not that attractive). Download

Sea Glass 
This is relatively anew theme under development. This one is among the best I’ve seen around. It that mocks Mac-kind look inspired by different colored stones. You can checkout the details here.

Info Look And Feel 
This one is based on the Metal look and feel. This is the one that you will find in most enterprise or commercial Java Apps. It’s designed to have a slim, clean appearance. It has support for themes. Works best for Windows, though looks decent on KDE as well. Download

Pgs Look And Feel 
I would call this a windows and KDE/Gnome hybrid. It aims be a very modern cross-platform LAF with nice features. the UI components are not as-sleek-as-others. Download

Quaqua Look And Feel 
The Quaqua LAF is an user interface library which adheres closest to Mac OS X. Download

Casual Themes

Oyaha
This one is a cool and trendy. It’s unique, as it features transparency, sounds and is Skinable. For the cool generations. Download

Liquid Look And Feel 
Liquid gives the application a crystal effect on the buttons. It’s based on Mosfet’s Liquid 0.9.6 theme for KDE 3.x. Reminds of Candy theme from StyleXP. Download

JTattoo 
JTattoo is skinnable and consists of several different LAF. User can customize the look by choosing among different available color schemes. Download

Make Java applications more attractive, and encourage Open Source, cheers.

I`ll keep on updating the list. Make sure you check back.

Do you know of any others? I`ll be happy to include them. Follow me on Twitter.