FREE:
http:www.sxc.hu
Some of the images can be very amiture, but you can find a whole lot of print quality (300DPI)
images for free, just notify the author.
Per Image/Premium:
http://www.stockxpert.com/
Great site includes vector/eps formats also!
You can even search for photos by color!
Another good site with extensive search capabilities.
http://www.istockphoto.com/index.php
Good for illistrations as well as photos.