http://www.pentagon-ai.army.mil/images/icons/misc/misc.html
As the title clearly states, this page is a resource for images that can be used a icons for a variety of miscellaneous subjects. In this collection, prepared by The U.S. Army Artificial Intelligence Center, icons of various sizes, colors and subjects are displayed along with their file names and URLs. Download the images you need and you will be assured the icon you want will be available at the time you need it.