DLS - US online digital media library including public domain images
images.fws.gov

Fotosearch - photo resource site with access to royalty free photographs
www.fotosearch.com

Freeimages - free stock photos online
www.freeimages.co.uk

Clip Art - royaly free clip art, animations, web graphics, photos and fonts
www.clipart.com

Science Photo Library - stock science images
www.sciencephoto.com

Shutterpoint - stock photography resource - buy or sell photos
www.shutterpoint.com