General:
Google Images - http://images.google.com
Yahoo Images - http://images.yahoo.com

Free:
FreePhotosBank - http://www.freephotosbank.com
FreeDigitalPhotos - http://www.greedigitalphotos.net
StockVault - http://www.stockvault.net
Open Stock Photography - http://www.openstockphotography.org
FreePhoto1.com - http://www.freephoto1.com
Creative Commons - http://creativecommons.org
BigFoto - http://www.bigfoto.com
MorgueFile - http://www.morguefile.com/
Flickr Creative Commons - http://www.flickr.com/creativecommons/
Image*After - http://www.imageafter.com/
Stock.Xchng - http://www.sxc.hu/index.phtml
EveryStockPhoto - http://www.everystockphoto.com/
FreePixels - http://www.freepixels.com/

Cost Associated:
iStockphoto Inc. - http://www.istockphoto.com/
Fotolia - http://us.fotolia.com/
Stockxpert - http://www.stockxpert.com/
Photospin - http://www.photospin.com
Photos.com - http://www.photos.com
Getty Images - http://www.gettyimages.com
Cartoonbank.com - http://www.cartoonbank.com/pro/
Comstock Images - http://www.comstock.com
ClipArt (and much more!) - http://www.clipart.com/en

*Familiarize yourself with the “Fair Use” provisions of copyright law and the “Terms of Use” sections of ALL the sources you use. You may need to seek permission or acknowledge the source before you can legally use some graphics.*