http://www.readwriteweb.com/archives/digital_image_resources_on_the_deep_web.php
Read Write Web

http://school.discoveryeducation.com/clipart/
Check out terms of use. Some citation and limitations are there.

http://www.phillipmartin.info/clipart/homepage.htm
Received permission from the artist.

http://www.openclipart.org/
No attribution required

http://office.microsoft.com/en-us/
Microsoft ClipGallery LiveProvided for the purpose of granting rights to licensed users of Microsoft Office. Examples of permissible use include, but are not limited to: newsletters, brochures, web sites, presentations, flyers, postcards, trade show materials, newspaper advertisements, product catalogs, and reports.

http://www.wpclipart.com/
Free public domain images safe for all students.

http://etc.usf.edu/clipart/
Free to use

http://www.teacherfiles.com/clip_art.htm
Free to use

http://www.pics4learning.com/
Permission is granted for students and teachers to use all of the images on this site.

http://www.sxc.hu/
High resolution, copyright free images

http://compfight.com/
Flickr Search Tool

http://www.iconfinder.com/
Icon Maker

http://commons.wikimedia.org
Many of the images used in wikipedia have been uploaded here.

http://www.zoo-m.com/flickr-storm/
Great for secondary students

http://www.morguefile.com
Nice resource of moderated photos, attribution highly encouraged

http://www.easystockphotos.com/
Easy Stock Photos is a good way to find royalty free Stock photos, pictures, images & information in the public domain.

http://public-domain.zorger.com/
Free public domain images available without copyright free for any use.

http://www.wpclipart.com/index.html
Free public domain images safe for all students

http://karenswhimsy.com/public-domain-images
Free to use, link back encouraged, but not required

http://animalphotos.info/a/
Free photos of animals

http://copyrightfriendly.wikispaces.com/
A HUGE collection of photos. Most are public domain. Check terms of use.

http://weblist.me/Copyright-friendly-image-search
Public Domain and free to use

http://worldimages.sjsu.edu/
Images for teachers and students to use in projects under Creative Commons license. Attribution required.

http://edupic.net/
Free photographs and drawings for teachers and students to use.

http://www.photos8.com/
Images in the public domain.