Pay sites
www.istockphoto.com
http://www.everystockphoto.com/
http://www.stockxpert.com/browse_image
http://www.photos.com/en/

Combination of Pay/Free
http://www.sxc.hu

Libraries
http://www.nla.gov.au/apps/picturescatalogue
http://www.pictureaustralia.org/

Free/Public Domain
http://meta.wikimedia.org/wiki/Help:Public_domain_image_resources
http://www.flickr.com/search/commons/?w=all&q=&m=text
http://dir.yahoo.com/Arts/Visual_Arts/Photography/Exhibits/Historic/
http://srufaculty.sru.edu/david.dailey/public/public_domain.htm
http://www.library.uni.edu/instruction/tips/guidepublicdomain.shtml
http://www.publicdomainpictures.net/
http://search.yahoo.com/search/dir?ei=UTF-8&p=public+domain+images&h=c
http://www.fromoldbooks.org/
http://www.pdphoto.org/
http://plants.usda.gov/gallery.html
http://mayang.com/textures/

Vector/clipart
http://vector4free.com/vectors
http://www.vecteezy.com/
http://123freevectors.com/
http://www.brandsoftheworld.com/