• Java look and feel Graphics Repository, but hope that someone add more modern icons!
• The Crystal SVG iconset for Linux are pretty good and have a fair number of toolbar icons. They're in .png format and so compatible with Java 1.3+. Not sure about the licence but they seem to be part of KDE and so GPL would be a reasonable assumption. These icons are rendered from SVG vector sources which can be found through the links at the bottom of the KDE Icon Guide (which is worth a read is you're designing your own icons)
• Foood's iCandy Junior icons are very good but only for personal use. They are not open source and cannot be distributed with applications. Use the Linux versions which are in .png format
• glyFX have a small free sample of toolbar icons and a good selection of commercial icons
• Ximian Icons http://developer.ximian.com/themes/icons/ooo-icons.html
• http://www.iconexperience.com/index.php

-- JoshuaMarinacci - 11 May 2004

• Dean S. Jones' Icon Collection is another good icon collection frequently used in Java applications.
• The Freehep Icon Browser is a useful tool for browsing through and selecting icons for your application.

-- TonyJohnson - 15 May 2004

• Nuvola icon theme is a great icon theme with a quality and range of icons comparable to the Crystal-icons by Everaldo. They're licensed under terms of LGPL.

-- Patrick Gotthardt - 04 April 2005