One great source of free graphics, that many people may overlook, is any GNU/Linux distro and all of the great GPL graphics on it. There are more graphics on these cds than are in most free graphic galleries. They can be modified, and used for both personal and commercial purposes. Just don't try to make one of them into your logo banner. Even if you modify it, any GPL licensed works must also be agin released under the same or similar license, so you would never be able to claim exclusive rights over it. But if the value of your website is in written content, and not graphical intellectual content, then this might be a great place for source graphic material.