Google Image search: http://www.google.com/imghp?hl=en
Flickr.com: The best way to store, search, sort, and share your photos: http://flickr.com/
Getty Images (most need to be purchased): http://creative.gettyimages.com/source/home/home.aspx
Free images: http://www.freeimages.co.uk/
AltaVista image search: http://www.altavista.com/image/default
Corbis (most need to be purchased): http://pro.corbis.com/
Live Weather Images: http://www.weatherimages.org/
Hubble Space Telescope Gallery: http://hubblesite.org/gallery/
Clip art: http://www.clipartconnection.com/
Comstock images: http://www.comstock.com/web/default.asp
Web Shots http://www.webshots.com/explore/gallery.html
TerraServer: Maps and aerial photos of most parts of the earth: http://terraserver.microsoft.com/
Ditto.com - the leading visual search engine (http://ditto.com/)
discovery School's Clip Art Gallery (http://school.discovery.com/clipart/index.html)
Awesome Clpart for Kids (http://www.awesomeclipartforkids.com/)
Cool Archive Free Clip Art and Fonts (http://coolarchive.com/)